Hard film for cutting tools, cutting tool coated with hard film, process for forming hard film and target used to form hard film

ABSTRACT

A hard film for cutting tools which is composed of 
 
(Ti 1-a-b-c-d , Al a , Cr b , Si c , B d )(C 1-e N e ) 
0.5≦a≦0.8, 0.06≦b, 0≦c≦0.1, 0≦d≦0.1, 0≦c+d≦0.1, a+b+c+d&lt;1, 0.5≦e≦1 (where a, b, c, and d denote respectively the atomic ratios of Al, Cr, Si, and B, and e denotes the atomic ratio of N.)

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hard film to improve the wearresistance of cutting tools such as tips, drills, and end mills, acutting tool coated with said hard film which exhibits excellent wearresistance, a process for forming said hard film, and a target used as avapor source to form said hard film.

2. Description of the Related Arts

It has been common practice to coat cutting tools made of cementedcarbide, cermet, or high speed tool steel with hard film of TiN, TiCN,TiAlN, or the like for the purpose of improving their wear resistance.

Because of its excellent wear resistance as disclosed in Japanese PatentNo. 2644710, the film of compound nitride of Ti and Al (referred to asTiAlN hereinafter) has superseded the film of titanium nitride, titaniumcarbide, or titanium carbonitride to be applied to cutting tools forhigh speed cutting or for high hardness materials such as quenchedsteel.

There is an increasing demand for hard film with improved wearresistance as the work material becomes harder and the cutting speedincreases.

It is known that the above-mentioned TiAlN film increases in hardnessand improves in wear resistance upon incorporation with Al. JapanesePatent No. 2644710 indicates that TiAlN precipitates soft AlN of ZnSstructure when the Al content therein is such that the compositionalratio x of Al exceeds 0.7 in the formula (Al_(x)Ti_(1-x))N representingTiAlN. The foregoing patent also mentions that “if the Al content (x)exceeds 0.75, the hard film has a composition similar to that of AlN andhence becomes soft, permitting the flank to wear easily”. In addition,the foregoing patent shows in FIG. 3 the relation between thecompositional ratio of Al and the hardness of film. It is noted that thehardness begins to decrease as the compositional ratio of Al exceedsabout 0.6. This suggests that AlN of ZnS structure begins to separateout when the compositional ratio of Al is in the range of 0.6-0.7 andAlN of ZnS structure separates out more as the compositional ratio of Alincreases further, with the result that the hardness of film decreasesaccordingly. Moreover, the foregoing patent mentions that the TiAlN filmbegins to oxidize at 800° C. or above when the compositional ratio x ofAl is 0.56 or higher, and this temperature rises according as the valuex increases. The temperature which the TiAlN film withstands withoutoxidation is about 850° C. when the compositional ratio of Al is 0.75(which is the upper limit for the TiAlN film to have adequate hardness).

In other words, the conventional TiAlN film cannot have both highhardness and good oxidation resistance because there is a limit toincreasing hardness by increasing the compositional ratio of Al.Consequently, it is limited also in improvement in wear resistance.

At present, cutting tools are required to be used at higher speeds forhigher efficiency. Cutting tools meeting such requirements need hardcoating film which has better wear resistance than before.

OBJECT AND SUMMARY OF THE INVENTION

The present invention was completed in view of the foregoing. It is anobject of the present invention to provide a hard film for cutting toolswhich is superior in wear resistance to TiAlN film and permitshigh-speed efficient cutting, a process for forming said hard film, anda target used to efficiently form a hard film for cutting tools by saidprocess.

The present invention is directed to a hard film for cutting toolscomposed of(Ti_(1-a-b-c-d), Al_(a), Cr_(b), Si_(c), B_(d))(C_(1-e)N_(e))

-   0.5≦a≦0.8, 0.06≦b, 0≦c≦0.1, 0≦d≦0.1,-   0≦c+d≦0.1, a+b+c+d<1, 0.5≦e≦1-   (where a, b, c, and d denote respectively the atomic ratios of Al,    Cr, Si, and B, and e denotes the atomic ratio of N. This is to be    repeated in the following.)

The present invention includes preferred embodiments in which the valueof e is 1, or the values of a and b are in the range of

-   0.02≦1−a−b≦0.30, 0.55≦a≦0.765, 0.06≦b, or-   0.02≦1−a−b≦0.175, 0.765≦a, 4(a−0.75)≦b.

According to the present invention, the hard film for cutting toolsshould preferably be one which has the crystal structure mainly ofsodium chloride structure. The sodium chloride structure shouldpreferably be one which has the (111) plane, (200) plane, and (220)plane such that the intensity of diffracted rays from them measured byX-ray diffraction (θ-2θ method), which is denoted by I(111), I(200), andI(220), respectively, satisfies expression (1) and/or expression (2) andexpression (3) given below.I(220)≦I(111)  (1)I(220)≦I(200)  (2)I(200)/I(111)≧0.1  (3)

In addition, the sodium chloride structure should preferably be onewhich, when measured by X-ray diffraction (θ-2θ method) with Cu Ka line,gives the diffracted ray from the (111) plane whose angle of diffractionis in the range of 36.5°-38.0°. Moreover, the diffracted ray from the(111) plane should preferably have a half width not larger than 1°.

The above-mentioned hard film for cutting tools can be used to obtaincoated cutting tools with outstanding wear resistance.

The present invention is directed also to a process for forming theabove-mentioned hard film for cutting tools. This process consists ofvaporizing and ionizing a metal in a film-forming gas atmosphere andconverting said metal and film-forming gas into a plasma, therebyforming a film. The process is an improved arc ion plating (AIP) methodwhich consists of vaporizing and ionizing a metal constituting a targetby arc discharge, thereby forming the hard film of the present inventionon a substrate, wherein said improvement comprises forming the magneticlines of force which:

-   -   a) are parallel to the normal at the target's evaporating        surface, and    -   b) run toward the substrate in the direction parallel to or        slightly divergent from the normal to the target's evaporating        surface, thereby accelerating the conversion of film-forming gas        into a plasma by the magnetic lines of force.        In this case, the bias voltage to be applied to the substrate        should preferably be −50V to −400V with respect to earth        potential. In addition, the substrate should preferably be kept        at 300-800° C. while film is being formed thereon. The reactant        gas for film forming should preferably have a partial pressure        or total pressure in the range of 0.5-7 Pa.

Incidentally, the reactant gas used in the present invention denotes anyone or more of gaseous nitrogen, methane, ethylene, acetylene, ammonia,and hydrogen, which contain elements necessary for coating film. Thereactant gas may be used in combination with a rare gas such as argon,which is referred to as an assist gas. The reactant gas and the assistgas may be collectively referred to as a film-forming gas.

The present invention is directed also to a target used to form hardfilm which is composed of Ti, Al, Cr, Si, and B and has a relativedensity higher than 95%. The target should preferably contain no poresor pores with a radius smaller than 0.3 mm.

The target should have a composition defined by(Ti_(1-x-y-z-w), Al_(x), Cr_(y), Si_(x), B_(w))

-   -   0.5≦x≦0.8, 0.06≦y, 0≦z≦0.1, 0≦w≦0.1,    -   0≦z+w≦0.1, x+y+z+w<1    -   (where x, y, z, and w denote respectively the atomic ratios of        Al, Cr, Si, and B. This is to be repeated in the following.) In        addition, if the value of (z+w) is 0, the values of x and y        should preferably be in the ranged defined below.

-   0.02≦1−x−y≦0.30, 0.55≦x≦0.765, 0.06≦y, or 0.02≦1−x−y≦0.175, 0.765≦x,    4(x−0.75)≦y.

Moreover, the target should preferably contain no more than 0.3 mass %oxygen, no more than 0.05 mass % hydrogen, no more than 0.2 mass %chlorine, no more than 0.05 mass % copper, and no more than 0.03 mass %magnesium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a triangular diagram showing the amount of metal componentsTi, Al, and Cr in the (Ti,Al,Cr)N film.

FIG. 2 is a schematic diagram showing an example of the arc ion plating(AIP) apparatus used to practice the present invention.

FIG. 3 is an enlarged schematic sectional diagram showing the importantpart of the arc evaporating source used to practice the presentinvention.

FIG. 4 is an enlarged schematic sectional diagram showing the importantpart of another arc evaporating source used to practice the presentinvention.

FIG. 5 is an enlarged schematic sectional diagram showing the importantpart of a conventional arc evaporating source.

FIG. 6 is an X-ray diffraction pattern of a film having a composition of(Ti_(0.1)Al_(0.7)Cr_(0.2))N. Part (1) is that of the film formed byusing the evaporating source of the present invention. Part (2) is thatof the film formed by using the conventional evaporating source.

FIG. 7 is a graph showing the relation between the substrate temperatureand the residual stress in the film having a composition of(Ti_(0.1)Al_(0.7)Cr_(0.2))N.

FIG. 8 is a diagram showing the range of the composition of metalliccomponents Ti, Al, and Cr of (Ti,Al,Cr)N film in Examples of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Under the above-mentioned circumstances, the present inventors conductedextensive studies to realize a hard film for cutting tools whichexhibits better wear resistance than before. As the result, it was foundthat the object is achieved if the film has both improved hardness andimproved oxidation resistance. The present inventors continued theirstudies with their attention paid to TiAlN film. It was found that theTiAlN film is greatly improved in hardness and oxidation resistance andhence in wear resistance if it is incorporated with Cr. It was alsofound that the TIAlN film is improved further in oxidation resistance ifit is incorporated with Si or B. Their quantitative investigations intothe effect of these additives led to the present invention.

The gist of the present invention resides in a hard film composed of(Ti_(1-a-b-c-d), Al_(a), Cr_(b), Si_(c), B_(d))(C_(1-e)N_(e))

-   0.5≦a≦0.8, 0.06≦b, 0≦c≦0.1, 0≦d≦0.1,-   0≦c+d≦0.1, a+b+c+d≦1, 0.5≦e≦1-   (where a, b, c, and d denote respectively the atomic ratios of Al,    Cr, Si, and B, and e denotes the atomic ratio of N.) A detailed    description is given below of the composition of the hard film.

TiAlN is a crystal of sodium chloride structure, or it is a compoundnitride of sodium chloride structure composed of TiN in which the Tisite is replaced by Al. The fact that AlN of sodium chloride structureis in an equilibrium state at a high temperature under a high pressuresuggests that it has a high hardness. Therefore, it would be possible toincrease the hardness of TiAlN film if the ratio of Al in TiAlN isincreased, with its sodium chloride structure maintained. However, AlNof sodium chloride structure is in a noneguilibrium state at normaltemperature under normal pressure or at a high temperature under a lowpressure. Consequently, ordinary gas-phase coating merely forms AlN ofZnS structure (which is soft) and never forms AlN of sodium chloridestructure as a simple substance.

Nevertheless, it is possible to form TiAlN of sodium chloride structureat normal temperature under normal pressure or at a high temperatureunder a low pressure, if nitride film is formed by incorporation of Alinto Ti, because TiN is of sodium chloride structure and has a latticeconstant close to that of AlN of sodium chloride structure and hence AlNis assimilated into the structure of TiN. However, as mentioned above,if the amount of Al in TiAlN exceeds a certain limit which is defined bythe compositional ratio (x) of 0.6-0.7 in (Al_(x),Ti_(1-x))Nrepresenting TiAlN, AlN of ZnS structure precipitates out because theeffect of assimilation by TiN is weak.

Incidentally, it would be possible to increase the ratio of AlN ofsodium chloride structure further if Ti in TiAlN is partly replaced byCr, because CrN has a lattice constant which is closer to that of AlN ofsodium chloride structure than that of TiN. If it is possible toincrease the ratio of AlN of sodium chloride structure in the film byincorporation with Cr as mentioned above, it seems possible to make itharder than TiAlN film.

On the other hand, Japanese Patent Laid-open No. 310174/1995 discloses amethod of increasing the hardness and oxidation resistance of TiAlN byincorporation with Si. The disclosed method requires that the amount ofAl be no more than 0.75 (in atomic ratio) and the amount of Si be nomore than 0.1 (in atomic ratio). If the amounts of Al and Si exceed theabove-specified limits, the resulting film takes on the hexagonalcrystal structure (which is soft). Therefore, further improvement inoxidation resistance is limited. By contrast, the present inventorsfound that it is possible to increase both oxidation resistance andhardness while maintaining the sodium chloride structure if the TiAlNfilm is incorporated with not only Cr but also Si. The behavior of Si isnot yet elucidated; presumably, it occupies the position of Ti in theTiN lattice just as in the case of Al in TiAlN.

Incidentally, because AlN, CrN, and SiN excels TiN in oxidationresistance, it is desirable to add Al, Cr, and Si more rather than Tifrom the view point of improving oxidation resistance.

A detailed explanation is given below of the reason why the atomicratios a, b, c, d, and e have been established for Ti, Al, Cr, Si, B,and C constituting the film of (Ti_(1-a-b-c-d), Al_(a), Cr_(b),Si_(c)B_(d))(C_(1-e)N_(e)).

First, Al should be added such that the lower limit and the upper limitof its atomic ratio (a) is 0.5 and 0.8, respectively, because a minimumamount of Al is necessary to secure oxidation resistance and hardnessand an excess amount of Al precipitates soft hexagonal crystals, therebylowering the hardness of film.

Cr permits the Al content to be increased while keeping the sodiumchloride structure as mentioned above. For this effect, Cr should beadded such that the lower limit of its atomic ratio (b) is 0.06.

The atomic ratio (a) of Al should be 0.55 or above, preferably 0.60 orabove. The lower limit of the atomic ratio (b) of Cr should preferablybe 0.08. In the case where the atomic ratio (a) of Al exceeds 0.765, theatomic ratio (b) of Cr should preferably be within the range mentionedbelow. In addition, since CrN is less hard than TiN, Cr will reducehardness if added excessively. Thus, the upper limit of the atomic ratio(b) of Cr should be 0.35, preferably 0.3.

FIG. 1 is a triangular diagram showing the amount of metal componentsTi, Al, and Cr in the (Ti,Al,Cr)N film. On the left-hand side of lineb=4(a−0.75) or in the area where b<4(a−0.75), the film hardness steeplydecreases because AlN in the film contains crystals of ZnS structure(which is soft) in higher ratio even though Cr is added. Therefore, inthe case where the atomic ratio (a) of Al exceeds 0.765, the ratio of Crshould preferably be b≧4(a−0.75).

Si produces the effect of improving oxidation resistance, as mentionedabove. B also produces a similar effect. Therefore, Si and/or B shouldbe added such that their atomic ratio (c+d) is 0.01 or above, preferably0.02 or above. On the other hand, excess Si and/or B separate out in theform of soft hexagonal crystals, thereby impairing wear resistance. Siand/or B should be added such that the upper limit of their atomicratios (c) and (d) or (c+d) is 0.1, preferably 0.07 or less, morepreferably 0.05 or less.

Incidentally, silicon nitride forms a compact protective film of siliconoxide in an oxidizing atmosphere at high temperatures, therebyprotecting the coating film from oxidation. On the other hand, boronnitride is inherently superior in oxidation resistance (with itsoxidation starting at about 1000° C.); however, its oxide is poor inprotecting power once oxidation has started. That is to say, boron isslightly inferior to silicon in oxidation resistance. Therefore, it isdesirable to add silicon alone instead of adding silicon and boron incombination.

The amount of Ti is determined by the amount of Al, Cr, Si, and B. TiNis harder than CrN, and the film will have a low hardness if Ti is notadded at all. Consequently, Ti should be added such that the lower limitof its atomic ratio (1-a-b-c-d) is 0.02, preferably 0.03. In the casewhere the atomic ratio of Al is 0.6 or above, the preferred amount of Tiis such that its atomic ratio is 0.35 or less, preferably 0.3 or less,because an excess amount of Ti relatively decreases the amount of Cr,thereby reducing the above-mentioned effect of assimilation.

Incidentally, in the case where Si and B are not contained or the valueof (c+d) is 0, the amount of Ti, Al, and Cr should be such that thevalues of (a) and (b) are within the range specified below.

-   0.02≦1−a−b≦0.30, 0.55≦a≦0.765, 0.06≦b, or-   0.02≦1−a−b≦0.175, 0.765≦a, 4(a−0.75)≦b.

If the atomic ratio of Ti is less than 0.20, the resulting film has muchimproved oxidation resistance, with the result that the temperature atwhich the film begins to oxidize increases. Therefore, the values of (a)and (b) in the range defined below is desirable.

-   0.02≦1−a−b<0.20, 0.55≦a≦0.765, 0.06≦b, or-   0.02≦1−a−b<0.20, 0.765≦a, 4(a−0.75)≦b.

If the atomic ratio (b) of Al is 0.6 or above and the upper limit of theatomic ratio (b) of Al is such that the resulting film is composedsolely of crystals of sodium chloride structure, the result is not onlygood oxidation resistance but also higher hardness thanTi_(0.4)Al_(0.6)N would have. (It is to be noted that Ti_(0.4)Al_(0.6)Nhas the highest hardness among those compounds represented by TiAlN inwhich 0.56≦Al≦0.75).

Therefore, the most desirable range of (a) and (b) is as follows.

-   0.02≦1−a−b<0.20, 0.60≦a≦0.709, or-   0.02≦1−a−b<0.20, 0.709≦a, 11/6x(a−0.66)≦b.    The above-mentioned preferred range is recommended particularly when    the value of (c+d) is 0.

As in the case mentioned above, the upper limit of the atomic ratio (b)of Cr should preferably be 0.35, preferably 0.3, because CrN is lesshard than TiN and excessive Cr lowers hardness.

Incorporation of C into the film causes hard carbides (such as TiC, SiC,and B₄C) to separate out, thereby making the film harder. The amount(1−e) of C should preferably equal the total amount (1−a−b) of Ti, Si,and B. Excessive C causes chemically unstable Al₄C₃ and Cr₇C₃ toseparate out, thereby deteriorating oxidation resistance. Therefore, Cshould be added such that the value of (e) in (Ti_(1-a-b-c-d), Al_(a),Cr_(b), Si_(c), B_(d))(C_(1-e)N_(e)) is 0.5 or above, preferably 0.7 orabove, more preferably 0.8 or above, and most desirably 1.

Incidentally, the hard film of the present invention should preferablybe composed mainly of crystals of sodium chloride structure, because itloses high strength if it contains crystals of ZnS structure.

The crystal in which the sodium chloride structure dominates is onewhich has the peak intensity of X-ray diffraction (θ-2θ method) definedby expression (4) below, whose value is 0.5 or above, preferably 0.8 orabove.[IB(111)+IB(200)+IB(220)+IB(311)+IB(222)+IB(400)]/[IB(111)+IB(200)+IB(220)+IB(311)+IB(222)+IB(400)+IH(100)+IH(102)+IH(110)]  (4)(where IB(111), IB(200), IB(220), IB(311), IB(222), and IB(400)represent respectively the peak intensity due to (111) plane, (200)plane, (220) plane, (311) plane, (222) plane, and (400) plane of sodiumchloride structure, and IH(100), IH(102), and IH(110) representrespectively the peak intensity due to (100) plane, (102) plane, and(110) plane of ZnS structure.)If the value of expression (4) is less than 0.5, the resulting film hasa hardness lower than that which is regarded as desirable in the presentinvention.

The peak intensity of ZnS structure is measured by using an X-raydiffractometer which emits Cu Ka line. The peak intensity is one whichappears at 2θ=32-33° for (100) plane, at 2θ=48-50° for (102) plane, orat 2θ=57-58° for (110) plane. Incidentally, although the crystal of ZnSstructure is composed mainly of AlN, its peak position actually measuredis slightly different from that shown in JCPDS cards because it containsTi, Cr, Si, and B.

The film of the present invention should preferably have the sodiumchloride structure such that the peak intensity measured by X-raydiffraction satisfies the following. I(220)≦I(111) and/or I(220)≦I(200)The reason for this is that the film has good wear resistance when the(111) plane or (0.200) plane (which is the closely packed plane ofsodium chloride structure) is parallel to the film surface.

The ratio of I(200)/I(111) should preferably be 0.1 or above (whereI(200) denotes the peak intensity due to (200) plane and I(11) denotesthe peak intensity due to (111) plane). This ratio varies in the rangeof about 0.1 to 5 depending on film-forming conditions, such as biasvoltage applied to the substrate, gas pressure, and film-formingtemperature. It was found in this invention that the film exhibits goodcutting characteristics when the ratio is 0.1 or above. A probablereason for this is as follows. It is considered that in the crystal ofsodium chloride structure, metal elements basically combine withnitrogen or carbon and there are very few metal-metal bonds,nitrogen-nitrogen bonds, and carbon-carbon bonds. Thus, metal atomsadjoin metal atoms, nitrogen atoms adjoin nitrogen atoms, and carbonatoms adjoin carbon atoms in the (111) plane, whereas metal atoms adjoinnitrogen atoms or carbon atoms in the (200) plane. There is a highpossibility that metal atoms combine with nitrogen atoms or carbon atomsin the (200) plane, and this leads to a good stability. Thus, it isexpected that if the stabler (200) plane is oriented at a certain ratiowith respect to the (111) plane, the resulting film has increasedhardness and exhibits improved cutting characteristics. The value ofI(200)/I(111) should be 0.3 or above, preferably 0.5 or above.

The angle of diffraction due to (111) plane varies depending on the filmcomposition, the state of residual stress, and the kind of substrate.The results of X-ray diffraction (θ-2θ method) with Cu Kα line indicatethat the hard film of the present invention varies in the angle ofdiffraction in the range of about 36.5-38.0° and that the angle ofdiffraction tends to decrease as the amount of Ti increases in the film.A probable reason why the angle of diffraction due to (111) planedecreases (or the distance between (111) planes increases) with theincreasing amount of Ti in the film is that the lattice constant (4.24Å) of TiN is larger than the lattice constant (4.12 Å) of AlN and thelattice constant (4.14 Å) of CrN of sodium chloride structure, asmentioned above. Incidentally, when the hard film of the presentinvention, which has the composition of(Ti_(0.12)Al_(0.70)Cr_(0.15)Si_(0.03))N, was formed on a cementedcarbide substrate, the angle of diffraction due to (111) plane varies inthe range of 36.6-37.1° depending on the film-forming conditions.

The angle of diffraction due to (111) plane of sodium chloride structurecan be calculated from the following Bragg's formula (5).2×(spacing of lattice planes, Å)×sin(angle of diffraction2θ/2)=wavelength of X-rays used (Å)  (5)The wavelength of X-rays is 1.54056 Å for Cu Kα line. Incidentally, thespacing of (111) planes in expression (5) can be calculated from thefollowing expression (6) which is obtained by using the law of mixturefrom the standard lattice constants (4.24 Å, 4.12 Å, and 4.14 Å) and thecompositional ratio of TiN, AlN, and CrN of sodium chloride structure.Spacing of (111) planes (Å)=[2.4492×Ti (at %)+2.379×Al (at %)+2.394×Cr(at %)]/100  (6)(The amount of each element is expressed in terms of 100% metallicelement.)

In the case where the hard film of the present invention, which has thecomposition of (Ti_(0.1)Al_(0.72)Cr_(0.18))N, is formed on a cementedcarbide substrate, the angle of diffraction obtained from theabove-mentioned expression (5) is 37.6°. In actual, however, the angleof diffraction varies in the range of 37.2-37.7° depending on thefilm-forming conditions and residual stress. The hard film of thepresent invention in its as-formed state receives compressive stress andhence the spacing of lattice planes parallel to the substrate is larger(due to Poisson effect) than that in the normal state or that calculatedform the above-mentioned expression (6). Therefore, the angle ofdiffraction due to (111) plane measured by X-ray diffraction (θ-2θmethod) was smaller than that in the normal state or that calculatedfrom the above-mentioned expression (5) by substituting the spacing oflattice plane in the normal state obtained from the above-mentionedexpression (6).

It is desirable that the angle of diffraction due to (111) planeobtained by X-ray diffraction (θ-2θ method) with Cu Kα line should bewithin ±0.3° of the standard angle of diffraction which is calculatedfrom the above-mentioned expressions (5) and (6) on the basis of thecomposition of metallic elements in the film.

The diffraction peak due to (111) plane has the property that its halfwidth varies depending on crystal size in the film and non-uniformresidual stress in the film and crystals in the film tend to becomesmall as the half width increases. [Half width usually denotes FWHM(Full Width Half Maximum) which is the width of that part of diffractionpeak at which the intensity is half the maximum intensity of thediffraction peak.] This half width is about from 0.2° to 1° in the caseof the hard film which satisfies the requirements of the presentinvention. In the case of hard film represented by(Ti_(0.1)Al_(0.72)Cr_(0.18))N (mentioned above), the half width rangesfrom 0.3° to 0.8° depending on the film-forming conditions.

The hard film of the present invention may be used in the form ofsingle-layer film which meets the above-mentioned requirements. It mayalso be used in the form of multi-layer film, each layer being mutuallydifferent and satisfying the above-mentioned requirements. The(Ti,Cr,Al,Si,B)(CN) film specified in the present invention, which is inthe form of single layer or multiple layers, may have on its one side orboth sides at least one layer composed of crystals in which the sodiumchloride structure dominates, which is selected from the groupconsisting of a layer of metal nitride, a layer of metal carbide, and alayer of metal carbonitride (which differ from the above-mentioned hardfilm in composition).

Incidentally, the “crystal in which the sodium chloride structuredominates” denotes the same one as defined above, which has the peakintensity of X-ray diffraction (θ-2θ method) defined by expression (4)given above, whose value is 0.8 or above. (with IB(111), IB(200),IB(220), IB(311), IB(222), and IB(400) representing respectively thepeak intensity due to (111) plane, (200) plane, (220) plane,

-   -   (311) plane, (222) plane, and (400) plane of sodium chloride        structure, and IH(100), IH(102), and IH(110) representing        respectively the peak intensity due to (100) plane, (102) plane,        and (110) plane of ZnS structure.) The layers of metal nitride,        metal carbide, and metal carbonitride (which are of sodium        chloride structure and differ from the above-mentioned hard film        in composition) include, for example, those films of TiN, TiAlN,        TiVAlN, TiCN, TiAlCN, TiNbAlCN, and TiC.

The hard film for cutting tools according to the present invention mayhave on its one side or both sides, in addition to the above-mentionedone or more layers, one or more layers of metal or alloy containing atleast one metal selected from the group consisting of 4A Group elements,5A Group elements, 6A Group elements, Al, and Si. The metals belongingto 4A Group, 5A Group, and 6A Group include Cr, Ti, and Nb. The alloyincludes Ti—Al. Such laminated film structure is effective forsubstrates made of ferrous material (such as HSS and SKD) which areinferior to those of cemented carbide in adhesion to the hard film. Thehard film with good adhesion to the substrate is obtained bysequentially forming on the above-mentioned ferrous substrate theabove-mentioned film of Cr, TiN, or TiAlN (which is less hard than thehard film specified in the present invention), an intermediate metallayer of Cr, Ti, or Ti—Al, and the hard film of the present invention.The intermediate layer which is relatively softer than the hard film ofthe present invention reduces residual stress, thereby improvingadhesion (peel resistance).

In the case where the hard film of the present invention consists ofmore than one layer, each layer may have a thickness in the range of0.005-2 μm; however, the hard film of the present invention shouldpreferably have a total thickness of from 0.5 μm to 20 μm regardless ofwhether it is of single-layer structure or composed of more than onelayer. The multiple-layer structure may be formed from (i) mutuallydifferent films each satisfying the requirements of the presentinvention, (ii) layers of metal nitride, metal carbide, or metalcarbonitride which are of sodium chloride structure and different fromthe above-mentioned hard film in composition, and (iii) layers of metalor alloy containing at least one metal selected from the groupconsisting of 4A Group elements, 5A Group elements, 6A Group elements,Al, and Si. With a total thickness less than 0.5 μm, the resulting hardfilm is too thin to have sufficient wear resistance. With a totalthickness more than 20 μm, the resulting hard film is liable to break orpeel during cutting. Therefore, a more preferable thickness is 1 μm ormore and 15 μm or less.

Incidentally, the cutting tools to be coated with the hard film of thepresent invention include end mills, drills, hobs, and throw-awayinserts which are made of cemented carbide, high speed steel (HSS),cermet, or CBN sintered body. Recently, cutting tools are used underseverer conditions than before as the work becomes harder and thecutting speed increases, and hence the coating film for them is requiredto have higher hardness and better oxidation resistance. The hard filmof the present invention satisfies both of these requirements. It ismost suitable for those cutting tools which are used under dry orsemi-dry cutting conditions. The conventional typical film of TiAlN doesnot exhibit sufficient oxidation resistance and hardness under drycutting conditions (in which the temperature is considerably high). Thisdrawback is overcome by the film of the present invention which has bothhigh hardness and good oxidation resistance.

The film of the present invention, whose crystal structure is dominatedsubstantially by sodium chloride structure despite its high Al content,may be formed effectively by the process specified in the presentinvention. This process consists of vaporizing and ionizing a metalconstituting a target by arc discharge in a film-forming gas atmosphereand converting said metal and film-forming gas into a plasma, therebyforming a film. The process should preferably be carried out in such away as to accelerate the conversion of film-forming gas into a plasma bythe magnetic lines of force which:

-   -   a) are parallel to the normal at the target's evaporating        surface, and    -   b) run toward the substrate in the direction parallel to or        slightly divergent from the normal to the target's evaporating        surface.

The arc ion plating (AIP) apparatus used in the process of the presentinvention differs from the conventional one, in which the source ofmagnetic field is placed behind the target and the component of magneticfield perpendicular to the target film is small. The apparatus used toform the hard film of the present invention is constructed such that themagnet is placed beside or in front of the target so that magnetic linesof force diverge approximately perpendicularly to or extend parallel tothe evaporating surface of the target. The magnetic lines of forceaccelerate the conversion of the film-forming gas into a plasma. This isvery effective in forming the hard film of the present invention.

An example of the AIP apparatus used to practice the present inventionis shown in FIG. 2. A brief description of the AIP apparatus is givenbelow.

The AIP apparatus consists of a vacuum chamber 1 (which has anevacuating port 11 connected to a vacuum pump and a supply port 12 tofeed a film-forming gas), an arc-vaporizing source 2 which vaporizes andionizes by arc discharge a target constituting a cathode, a holder 3 tohold a substrate W (cutting tool) to be coated, and a bias power source4 to apply through the holder 3 a negative bias voltage to the substrateW across the holder 3 and the vacuum chamber 1.

The arc-vaporizing source 2 is provided with a target 6 constituting acathode, an arc power source 7 connected to the target 6 and the vacuumchamber 1 constituting an anode, and a permanent magnet 8 to generate amagnetic field forming magnetic lines of force which divergeapproximately perpendicularly to or extend parallel to the evaporatingsurface of the target and reach the vicinity of the substrate W. Themagnetic field should be such that its magnetic flux density is higherthan 10 G (Gauss), preferably higher than 30 G, at the center of thesubstrate. Incidentally, the term “approximately perpendicularly to theevaporating surface” means an angle of from 0° to about 30° with respectto the normal to the evaporating surface.

FIG. 3 is an enlarged sectional schematic diagram showing the importantpart of the arc evaporating source used to practice the presentinvention. The above-mentioned magnet 8 to generate a magnetic field isso arranged as to surround the evaporating surface S of the target 6.The magnet is not a sole means to generate a magnetic field; it may bereplaced by an electromagnet consisting of a coil and an electricsource. Alternatively, the magnet may be so placed as to surround thefront (facing the substrate) of the evaporating surface S of the target6, as shown in FIG. 4. Incidentally, although the vacuum chamber in FIG.1 functions as an anode, it is also possible to provide a specialcylindrical anode which surrounds the side front of the target.

Incidentally, FIG. 5 shows a conventional AIP apparatus, in which thearc evaporating source 102 is provided with an electromagnet 109 toconcentrate the arc discharge onto the target 106. However, since theelectromagnet 109 is placed behind the target 106, the magnetic lines offorce become parallel to the target surface in the vicinity of thetarget evaporating surface and hence do not reach the vicinity of thesubstrate w.

The arc evaporating source of the AIP apparatus used in the presentinvention differs from the conventional one in the structure of magneticfield and hence in the way the plasma of film-forming gas expands.

The evaporating source shown in FIG. 4 converts the film-forming gasinto plasma as the result of arc-induced electrons (e) partly windingaround the magnetic line of force and colliding with nitrogen moleculesconstituting the film-forming gas. By contrast, the conventionalevaporating source 102 shown in FIG. 5 works differently. That is, themagnetic lines of force are confined near the target and hence theplasma of film-forming gas generated as mentioned above has the highestdensity near the target and a low density near the substrate W. However,in the case of the evaporating source shown in FIGS. 3 and 4, which isused in the present invention, the magnetic line of force reach thesubstrate W, so that the plasma of film-forming gas has a much higherdensity near the substrate W than that in the case of conventionalevaporating source. It is considered that the different in plasmadensity affects the crystal structure of the film formed.

An example of such effects actually observed is shown in FIG. 6, whichis an X-ray diffraction pattern of a TiCrAlN film (having a compositionof (Ti_(0.1)Cr_(0.2)Al_(0.7))N) which was prepared by using theconventional evaporating source and the improved evaporating source ofthe present invention. In FIG. 6 “B1” represents the sodium chloridestructure and “Hex” represents the ZnS structure and “( )” representsthe crystal plane. In addition, unmarked peaks in FIG. 6 are ascribed tothe substrate (cemented carbide). Both of the evaporating sources wereoperated to form film samples under the following conditions. Arccurrent: 100 A, pressure of nitrogen gas: 2.66 Pa, substratetemperature: 400° C., and bias voltage for substrate: varied from 50V to300V. Incidentally, the bias voltage is negative with respect to earthpotential. Thus, a bias voltage of 100V, for example, means a biasvoltage which is −100V with respect to earth potential.

The evaporating source of the conventional AIP apparatus, in which themagnet is placed behind the target, yields a film which is composed ofmixed phases of cubic system (sodium chloride structure) and hexagonalsystem (ZnS structure) even when the bias voltage is increased to 300V,as shown in FIG. 6(2). By contrast, the evaporating source of the AIPapparatus of the present invention, in which the magnet is placed besidethe target, yields a film which is composed of single phase of sodiumchloride structure when the bias voltage is 70V or higher with respectto earth potential, as shown in FIG. 6(1).

AlN of sodium chloride structure is inherently in a non-equilibriumstate at normal temperature under normal pressure, and hence it is asubstance which does not form readily. Nevertheless, it is consideredthat the evaporating source of the present invention actively convertsnitrogen into plasma and the resulting high-energy nitrogen particleshelp to form the AlN of sodium chloride structure in a non-equilibriumstate.

The higher is the bias voltage, the higher becomes the energy offilm-forming gas and metal ions which have been converted into plasma,and the crystals of the film take on sodium chloride structure morereadily. Consequently, the bias voltage should be 50V or higher,preferably 70V or higher, and more preferably 100V or higher. However,an excessively high bias voltage is not practical because the film isetched by the film-forming gas which has been converted into plasma andhence the film-forming rate is extremely small. Consequently, the biasvoltage should be 400V or lower, preferably 300V or lower, morepreferably 260V or lower, and most desirably 200V or lower.Incidentally, the bias voltage is negative with respect to earthpotential. Thus, a bias voltage of 100V, for example, means a biasvoltage which is −100V with respect to earth potential. The object ofapplying a bias voltage is to impart energy to the incident film-forminggas and metal ions from the target, thereby allowing the film to take onthe sodium chloride structure. The preferred range of the bias voltagevaries depending on the composition of the film to be formed. In thecase of film with a comparatively low Al content or a comparatively highCr content, a comparatively low bias voltage will work owing to theabove-mentioned assimilating effect which contribute to sodium chloridestructure. If the Al content is less than about 65 atom % or the Crcontent is more than about 25 atom %, it is possible to obtain asingle-layer film of sodium chloride structure even when the biasvoltage is 70V or lower.

According to the present invention, the substrate temperature should bein the range of 300-800° C. at the time of film forming. This is relatedwith the stress of the resulting film.

FIG. 7 is a graph showing the relation between the substrate temperatureand the residual stress of the resulting film having a composition of(Ti_(0.1)Al_(0.7)Cr_(0.2))N. The film was formed under the followingconditions. Arc current: 100 A, bias voltage for the substrate: 150V,and pressure of nitrogen gas: 2.66 Pa.

It is noted from FIG. 7 that the residual stress in the resulting hardfilm decreases according as the substrate temperature increases. Theresulting film with excessive residual stress is poor in adhesion andliable to peeling. Consequently, the substrate temperature should be300° C. or higher, preferably 400° C. or higher. On the other hand, thehigher the substrate temperature, the less the residual stress. However,the film with excessively small residual stress is poor in compressivestrength and hence less effective in increasing the resistance of thesubstrate to bending. It also causes thermal change to the substrate dueto high temperature. Consequently, the substrate temperature should be800° C. or lower, preferably 700° C. or lower.

In the case where the substrate is cemented carbide, the above-mentionedsubstrate temperature is not specifically restricted. However, in thecase where the substrate is high speed tool steel (such as JIS-HSS andJIS-SKH51) and hot work tool steel (such as JIS-SKD11 and JIS-SKD61),the substrate temperature at the time of film forming should be lowerthan the tempering temperature so that the substrate retains itsmechanical properties. The tempering temperature varies depending on thesubstrate material; it is about 550-570° C. for JIS-SKH51, 550-680° C.for JIS-SKD61, and 500-530° C. for JIS-SKD11. The substrate temperatureshould be lower than the tempering temperature, preferably lower thanthe tempering temperature by about 50° C.

According to the present invention, the film should preferably be formedsuch that the reactant gas has a partial pressure or total pressure inthe range of from 0.5 Pa to 7 Pa. The pressure of the reactant gas isexpressed in terms of “partial pressure or total pressure” because thereactant gas may or may not contain an assist gas. The reactant gaswithout assist gas is nitrogen or methane which contains elementsessential for the film. The assist gas is a rare gas such as argon. Inthe case where the film is formed from the reactant gas without assistgas, it is necessary to control the total pressure of the reactant gas.In the case where the film is formed from the reactant gas with anassist gas, it is necessary to control the partial pressures of both thereactant gas and the assist gas. If the partial pressure or totalpressure of the reactant gas is lower than 0.5 Pa, evaporation by arcgives rise to a large amount of macroparticles (resulting from moltentarget), making the film surface rough, which is undesirable for someapplications. On the other hand, if the partial pressure or totalpressure of the reactant gas is higher than 7 Pa, the reactant gasscatters evaporated particles due to frequent collision, therebylowering the film-forming rate. Therefore, the partial or total pressureof the reactant gas should be from 1 Pa to 5 Pa, preferably from 1.5 Pato 4 Pa.

In the present invention, the AIP method is used for film forming, andit has been explained above. The film-forming method is not restrictedto AIP; any method can be used so long as it efficiently converts themetallic elements and the reactant gas into plasma. Such additionalmethods include pulse sputtering and nitrogen ion beam assisteddeposition.

The hard film of the present invention may be effectively produced byvapor-phase coating such as ion-plating and sputtering in which a targetis vaporized or ionized so as to form a film on the substrate, asmentioned above. Any target lacking desirable properties does not permitstable discharging at the time of film forming; therefore, the resultingfilm is poor in the uniformity of composition. The present inventors'investigation on the target properties necessary for the hard film withgood wear resistance revealed the following.

First, the target should have a relative density not lower than 95%.This condition is necessary to provide stable discharging at the time offilm forming and to efficiently yield the hard film of the presentinvention. With a relative density lower than 95%, the target has acoarse portion such as micropores in the alloy component. A target withsuch an alloy component does not evaporate uniformly, and hence theresulting film varies in composition and thickness. In addition, porousportions consume locally and rapidly, thereby reducing the target life.A target with a large number of voids not only rapidly consumes but alsocracks due to loss of strength. The relative density of the targetshould preferably be 96% or higher, more preferably 98% or higher.

Even though a target has a relative density not lower than 95%, it maynot yield a good film (due to unstable discharging) if it has largevoids. It is known that a target with voids larger than 0.5 mm in radiusdoes not permit continuous film forming because arc discharging isinterrupted by the alloy component evaporating or ionizing. The presentinventors' investigation revealed that discharging is unstable, althoughnot interrupted, if there are voids not smaller than 0.3 mm in radius.Therefore, for stable discharging and efficient satisfactory filmforming, it is desirable that voids in a target should be smaller than0.3 mm in radius, preferably 0.2 mm or smaller in radius.

In vapor phase coating by the AIP method, the composition of the targetused determines the composition of the film formed. Therefore, it isdesirable that the composition of the target should be identical withthe composition of the intended film. In order to obtain the hard filmof the present invention which is superior in wear resistance, it isnecessary to employ a target having the composition of (Ti_(1-x-y-z-w),Al_(x), Cr_(y), Si_(z), B_(w)) 0.5≦x≦0.8, 0.06≦y, 0≦z≦0.1, 0≦w≦0.1,0≦z+w≦0.1, x+y+z+w<1 (where x, y, z, and w denote respectively theatomic ratios of Al, Cr, Si, and B. This is to be repeated in thefollowing.)

In the case where the hard film of the present invention does notcontain Si and B, the values of x, y, z, and w should preferably be inthe range defined below.

-   0.02≦1−x−y≦0.30, 0.55≦x≦0.765, 0.06≦y, z+w=0,-   or 0.02≦1−x−y≦0.175, 0.765≦x, 4(x−0.75)≦y, z+w=0.

In addition to meeting the above-mentioned requirements for composition,the target should have a uniform distribution of composition. Otherwise,the resulting hard film lacks uniformity in the distribution ofcomposition and hence varies in wear resistance from one part toanother. In addition, a target with varied distribution of compositionsuffers local variation in electrical conductivity and melting point.This leads to unstable discharging and hence to a poor film.Consequently, the target of the present invention should have a uniformdistribution of composition whose variation is within 0.5 atom %.

The present inventors also investigated how the discharging state at thetime of film forming varies depending on the amount of inevitableimpurities (such as oxygen, hydrogen, chlorine, copper, and magnesium)entering the target from the raw material or the atmosphere in which thetarget is produced.

As the result it was found that a target containing oxygen, hydrogen,and chlorine in large amounts explosively releases these gases,resulting in unstable discharging and, in the worst case, breakingitself, making film forming impossible. Therefore, it is desirable thatthe target contain oxygen, hydrogen, and chlorine in a limited amountnot more than 0.3 mass %, 0.05 mass %, and 0.2 mass %, respectively. Thepreferred content of oxygen, hydrogen, and chlorine should be not morethan 0.2 mass %, 0.02 mass %, and 0.15 mass %, respectively.

Copper and magnesium are also detrimental impurities because they aremore volatile (with a higher vapor pressure) than Ti, Al, Cr, Si, and Bconstituting the target of the present invention. When contained inlarge amounts, they form voids in the target at the time of filmforming, and such voids make discharging unstable during film forming.Therefore, the content of copper in a target should be 0.05 mass % orless, preferably 0.02 mass % or less. The content of magnesium in atarget should be 0.03 mass % or less, preferably 0.02 mass % or less.

One way to reduce the content of impurities as specified above is byvacuum melting of raw material powder or by mixing of raw materialpowder in a clean atmosphere.

In the meantime, the present invention does not specify the method ofpreparing the target. However, there is a preferred method whichconsists of uniformly mixing raw material powers in an adequate ratio byusing a V-blender or the like and then subjecting the resulting mixtureto CIP (cold isostatic pressing) or HIP (hot isostatic pressing). Theraw material powder is composed of Ti powder, Cr powder, Al powder, Sipowder, and B powder which have an adequately controlled particle size.Other methods include hot extrusion and super-high pressure hotpressing.

Although it is possible to produce a target from the mixed powder by hotpressing (HP), the resulting target does not have a sufficiently highrelative density because Cr is a high-melting metal. Instead ofproducing a target from a mixed powder as mentioned above, it is alsopossible to produce a target from a previously alloyed powder, by meansof CIP or HIP, or through melting and solidifying. The CIP or HIP withan alloy powder offers the advantage that the resulting target has auniform composition; however, it also suffers the disadvantage that theresulting target tends to have a low relative density because the alloypowder is poor in sinterability. The method involving the melting andsolidifying of an alloyed powder offers the advantage that the resultingtarget has a comparatively uniform composition but has the disadvantagethat the resulting target is subject to cracking and shrinkage cavity atthe time of solidification. It does not easily yield the target of thepresent invention.

EXAMPLE

The invention will be described in more detail with reference to thefollowing examples, which are not intended to restrict the scopethereof. Various changes and modifications may be made to the exampleswithout departing from the spirit and scope of the invention.

Example 1

A target of alloy composed of Ti, Cr, and Al was mounted on the cathodeof the AIP apparatus shown in FIG. 2. A substrate was mounted on theholder. The substrate is a chip of cemented carbide, a square end millof cemented carbide (10 mm in diameter, with two edges), or a piece ofplatinum foil (0.1 mm thick). The chamber was evacuated to a degree ofvacuum lower than 3×10⁻³ Pa while the substrate was being heated to 400°C. by means of a heater placed in the chamber. The substrate was given abias voltage of 700V in an argon atmosphere at 0.66 Pa, so that thesubstrate was cleaned with argon ions for 10 minutes. Subsequently,nitrogen gas was introduced into the chamber. With the chamber pressurekept at 2.66 Pa, an arc current of 100 A was applied for film forming. A4-μm thick film was formed on the surface of the substrate.Incidentally, a bias voltage of 150V was applied to the substrate sothat the substrate was kept negative with respect to earth potentialduring film forming.

After the film-forming step was complete, the resulting film wasexamined for composition of metal components, crystal structure, Vickershardness, and oxidation starting temperature. Vickers hardness wasmeasured by using a microvickers tester under a load of 0.25N for 15seconds. The composition of Ti, Cr, and Al in the film was determined byEPMA. The content of metal elements and impurity elements (such as O andC, excluding N) in the film was also determined by EPMA. It was foundthat the content of oxygen is less than 1 atom % and the content ofcarbon is less than 2 atom %. The crystal structure of the film wasidentified by X-ray diffraction. The oxidation starting temperature wasmeasured as follows by using the platinum sample. The platinum samplewas heated in a dry air from room temperature at a rate of 5° C./min byusing a thermobalance. The temperature at which the weight changes ismeasured and it is regarded as the oxidation starting temperature. Thevalue in the foregoing expression (4) was obtained by measuring theintensity of peaks due to respective crystal planes by using an X-raydiffractometer with Cu Ka line. Table 1 shows the thus obtained results(including composition of film, crystal structure, Vickers hardness,oxidation starting temperature, and the value of expression (4)). TABLE1 Oxidation starting Experiment Metals in film (atomic ratio) Vickerstemperature Crystal Value of No. Ti Cr Al hardness (° C.) structure *expression (4) 1 0.27 0.07 0.66 3090 850 B1 1 2 0.21 0.08 0.71 3010 880B1 + Hex 0.83 3 0.19 0.07 0.74 2960 900 B1 + Hex 0.81 4 0.09 0.15 0.762950 920 B1 + Hex 0.86 5 0.02 0.19 0.79 2900 960 B1 + Hex 0.82 6 0.180.12 0.70 3300 880 B1 1 7 0.09 0.19 0.72 3500 910 B1 1 8 0.04 0.21 0.753300 940 B1 1 9 0.28 0.12 0.60 3080 850 B1 1 10 0.18 0.20 0.62 3200 870B1 1 11 0.11 0.22 0.67 3340 890 B1 1 12 0.10 0.28 0.62 3130 870 B1 1 130.04 0.28 0.68 3210 910 B1 1 14 0.04 0.33 0.63 3110 880 B1 1 15 0.170.25 0.58 3050 860 B1 1 16 0.10 0.34 0.56 3020 860 B1 1 17 0.04 0.380.58 3030 870 B1 1 18 0.32 0.10 0.58 2870 830 B1 1 19 0.22 0.26 0.522920 830 B1 1 20 0.04 0.43 0.53 2820 840 B1 1 21 0.44 0 0.56 2700 800 B11 22 0.40 0 0.60 3050 820 B1 1 23 0.25 0 0.75 2700 850 B1 1 24 0.17 0.050.78 2300 900 B1 + Hex 0.55 25 0.10 0.10 0.80 2200 930 B1 + Hex 0.35 260.03 0.17 0.80 2500 960 B1 + Hex 0.75 27 0 0.25 0.75 2650 950 B1 1* B1 represents sodium chloride structure, and Hex represents ZnSstructure.

It is noted from Table 1 that the samples of TiAlN (0.56≦Al≦0.75) inExperiment Nos. 21, 22, and 23 have a film hardness of 2700-3050 and anoxidation stating temperature of 800-850° C. However, they do not haveboth improved film hardness and oxidation starting temperature. Bycontrast, the samples of Experiment Nos. 1 to 17, which have thecomposition as specified in the present invention, have a high Vickershardness as well as a high oxidation starting temperature.

The composition for metal components Ti, Al, and Cr in the (Ti,Al,Cr)Nfilm is shown in FIG. 8. Each composition is indicated by the sample No.(1 to 27). Samples Nos. 1 to 17 (marked with ●, ▴, and ▪), which arewithin the range specified by the present invention, has both the highhardness and the high oxidation starting temperature characteristic ofTiAlN (0.56≦Al≦0.75). In particular, samples Nos. 3 to 5 (marked with▪), which have a composition within the desirable range, have a highoxidation starting temperature, which is almost comparable to that ofTiAlN (0.56≦Al≦0.75) and also has a very high hardness. Samples Nos. 15to 17 have a hardness equivalent to the highest hardness of TiAlN(0.56≦Al≦0.75) and also a high oxidation starting temperature.

Samples Nos. 6 to 9 and 10 to 14 (marked with ●), which have acomposition within the desirable range, has the highest hardness and thehighest oxidation starting temperature which have never been attained bythe conventional TiAlN (0.56≦Al≦0.75) film. They exhibit better wearresistance than the conventional TiAlN (0.56≦Al≦0.75) film.

By contrast, samples Nos. 18 to 20 and 24 to 27 (marked with ◯), whichhave a composition outside the range specified in the present invention,do not have a high hardness and a high oxidation starting temperature atthe same time. They are equivalent to or inferior to the conventionalTiAlN (0.56≦Al≦0.75) film and hence they are not expected to have betterwear resistance than the conventional TiAlN (0.56≦Al≦0.75) film.

Example 2

Samples Nos. 1, 4, 7, 11, 16, 18, 19, 22, 24, and 27 in Example 1, whichare end mills coated with the hard film, were tested for wear resistanceby cutting several works of quenched JIS-SKD61 (HRC50) under thefollowing conditions.

-   -   Cutting speed: 20 m/min    -   Feed speed: 0.07 mm/edge    -   Depth of cut: 5 mm    -   Pick feed: 1 mm    -   Cutting oil: air blow only    -   Cutting direction: down cutting

After cutting over a length of 20 meters, the cutting edge of the endmill was examined under an optical microscope to measure the worn width.The results are shown in Table 2. TABLE 2 Experiment No. Worn width (μm)1 38 4 32 7 24 11 26 16 33 18 59 19 55 22 48 24 73 27 52It is noted from Table 2 that the samples of end mills Nos., 1, 4, 7, 11and 16, which are coated with the film meeting the requirements of thepresent invention, are superior in wear resistance (in terms of wornwidth) to the samples Nos. 18, 19, 22, 24, and 27, which are coated withthe film not meeting the requirements of the present invention.

Example 3

A target of alloy composed of Ti, Cr, Al, and Si was mounted on thecathode of the AIP apparatus shown in FIG. 2. A substrate was mounted onthe holder. The substrate is a chip of cemented carbide, a square endmill of cemented carbide (10 mm in diameter, with four edges), or apiece of platinum foil (0.2 mm thick). The chamber was evacuated to adegree of vacuum lower than 3×10⁻³ Pa while the substrate was beingheated to 550° C. by means of a heater placed in the chamber. Thesubstrate was cleaned with argon ions for 10 minutes. Subsequently,nitrogen gas or a mixture gas of nitrogen and methane was introducedinto the chamber. With the chamber pressure kept at 2.66 Pa, an arccurrent of 100 A was applied for film forming. An approximately 3-μmthick film was formed on the surface of the substrate. Incidentally, abias voltage of 100-200V was applied to the substrate so that thesubstrate was kept negative with respect to earth potential during filmforming.

After the film-forming step was complete, the resulting film wasexamined for composition of metal components, crystal structure, Vickershardness, and oxidation starting temperature. The composition of Ti, Cr,Al, and Si in the film was determined by EPMA (with mass absorptioncoefficient corrected). The content of metal elements and impurityelements (such as O and C, excluding N) in the film was also determinedby EPMA. It was found that the content of oxygen is less than 1 atom %and the content of carbon is less than 2 atom % (in the case wheremethane was not used as the film-forming gas). The resulting film wasexamined for crystal structure, Vickers hardness (under a load of0.25N), and oxidation starting temperature in the same way as inExample 1. Table 3 shows the thus obtained results (includingcomposition of film, crystal structure, Vickers hardness, oxidationstarting temperature, and the value of expression (4)). TABLE 3Oxidation starting Experiment Composition (atomic ratio) Vickerstemperature Crystal Value of No. Ti Cr Al Si C N hardness (° C.)structure * expression (4) 1 0.73 0 0.25 0.02 0.00 1.00 2500 700 B1 1 20.37 0.20 0.40 0.03 0.00 1.00 2600 750 B1 1 3 0.02 0.10 0.85 0.03 0.001.00 2000 1100 B1 + Hex 0.1 4 0.05 0.10 0.70 0.15 0.00 1.00 2200 1050B1 + Hex 0.1 5 0.10 0.18 0.72 0.00 0.00 1.00 2900 950 B1 1 6 0.12 0.150.70 0.03 0.60 0.40 3000 750 B1 1 7 0.30 0.18 0.50 0.02 0.00 1.00 2950950 B1 1 8 0.11 0.15 0.71 0.03 0.00 1.00 3300 1150 B1 1 9 0.04 0.20 0.700.06 0.00 1.00 3050 1100 B1 1 10 0.13 0.15 0.70 0.02 0.00 1.00 3200 1150B1 1 11 0.18 0.08 0.71 0.03 0.00 1.00 3100 1100 B1 1 12 0.18 0.08 0.710.03 0.20 0.80 3100 1050 B1 1 13 0.18 0.08 0.71 0.03 0.40 0.60 3020 1020B1 1 14 0.08 0.25 0.65 0.02 0.00 1.00 3050 1050 B1 1 15 0.07 0.30 0.600.03 0.00 1.00 3000 1000 B1 1 16 0.20 0.13 0.65 0.02 0.00 1.00 3030 980B1 1 17 0.25 0.12 0.60 0.03 0.00 1.00 3000 970 B1 1* B1 represents sodium chloride structure, and Hex represents ZnSstructure.

It is noted from Table 3 that the sample of TiAlSiN (0.05≦Al≦0.75) inExperiment No. 1 has neither improved hardness nor improved oxidationstating temperature. It is also noted that the samples Nos. 2, 3, 4, and6, which do not meet the requirements of the present invention, are poorin either film hardness or oxidation starting temperature. By contrast,the samples of Experiment Nos. 5 and 7 to 17, which have the compositionas specified in the present invention, have a high Vickers hardness aswell as a high oxidation starting temperature.

Example 4

Samples Nos. 3, 5, 8, 10, 12, 15, and 16, in Example 3, which are endmills coated with the hard film, were tested for wear resistance bycutting several works of quenched JIS-SKD61 (HRC50) under the followingconditions.

-   -   Cutting speed: 200 m/min    -   Feed speed: 0.05 mm/edge    -   Depth of cut: 5 mm    -   Pick feed: 1 mm    -   Cutting oil: air blow only    -   Cutting direction: down cutting

After cutting over a length of 30 meters, the cutting edge of the endmill was examined under an optical microscope to measure the worn width.The results are shown in Table 4. TABLE 4 Experiment No. Worn width (μm)3 35 5 25 8 15 10 13 12 17 15 20 16 19Noted from Table 4 that the samples of end mills Nos. 5, 8, 10, 12, 15and 16, which are coated with the film meeting the requirements of thepresent invention, are superior in wear resistance (in terms of wornwidth) to the sample No. 3, which is coated with the film not meetingthe requirements of the present invention.

Example 5

Using a target of alloy composed of Ti (9 at %), Cr (19 at %), and Al(72 at %), a square end mill of cemented carbide (10 mm in diameter,with two edges) was coated with a film a TiCrAlN (varying in thicknessas shown in Table 5) in the same way as in Example 1, except that thelength of film-forming time was changed. The vaporizing source shown inFIG. 4 was used. The metal components of the film were analyzed by EPMA.The composition was found to be Ti: 10 at %, Cr: 20 at %, and Al: 70 at%. The coated end mill was examined for wear resistance by cutting testin the same way as in Example 2. The results are shown in Table 5. TABLE5 Experiment No. Film thickness (μm) Worn width (μm) 1 0.9 30 2 2 24 3 425 4 10 20 5 18 20 6 0.3 55 7 21 NoteNote:The edge broke after cutting over a length of 15 meters.

It is noted from Table 5 that the samples Nos. 1 to 5, which have anadequate film thickness as specified in the present invention, exhibitgood wear resistance (in terms of worn width). The sample No. 6, whichhas a small film thickness, is poor in wear resistance. The Sample No.7, which has an excessive film thickness, broke during cutting.

Example 6

Film coating was performed on a substrate (a chip of cemented carbide, asquare end mill of cemented carbide (10 mm in diameter, with two edges),or a piece of platinum foil (0.1 mm thick)) which is placed on theholder in the AIP apparatus shown in FIG. 2, by using a target of alloycomposed of Ti (13 at %), Cr (15 at %), and Al (72 at %). With thevacuum chamber evacuated, the substrate was heated to 550° C. by meansof a heater placed in the chamber. A mixture gas of nitrogen and methanewas introduced into the chamber so that the pressure in the chamber waskept at 2.66 Pa. An arc current of 100 A was applied for film forming.On the substrate was formed a (TiAlCr)(CN) film (3 μm thick). Duringfilm forming, a bias voltage of 150V was applied to the substrate so asto keep it negative with respect to earth potential. Other film-formingconditions are the same as those in Example 1. After the film-formingstep was complete, the resulting film was examined for composition ofmetal components, oxidation starting temperature, and wear resistance.The composition of Ti, Al, and Cr in the film was determined by EPMA.The content of metal elements and impurity elements (excluding C and N)in the film was also determined by EPMA. It was found that the contentof oxygen is less than 1 atom %. The oxidation starting temperature wasmeasured in the same way as in Example 1. The coated end mill wasexamined for wear resistance by cutting test in the same way as inExample 2. The results are shown in Table 6. TABLE 6 Oxidation Wornstarting Experi- Film composition (atomic ratio) width temperature mentNo. Ti Al Cr C N (μm) (° C.) 1 0.14 0.69 0.17 0.1 0.9 23.0 950 2 0.140.69 0.17 0.3 0.7 25.0 930 3 0.14 0.69 0.17 0.4 0.6 28.0 920 4 0.14 0.690.17 0.6 0.4 45.0 800Target: TiAlCr (Ti:Al:Cr = 13:72:15)

It is noted from Table 6 that the end mill samples Nos. 1 to 3, whichare coated with a film meeting the requirements of the presentinvention, have a higher oxidation starting temperature and better wearresistance (in terms of worn width) in cutting test than the end millsample No. 4, which is coated with a (TiAlCr)(CN) film containing C andN in a ratio outside the range specified in the present invention.

Example 7

Film coating (approximately 3.5 μm thick) was performed on substrates byusing the AIP apparatus shown in FIG. 2. The substrates, the compositionof film, and the composition of alloy targets are shown below.

Substrates:

Chips of cemented carbide (for measurement of composition) Throw-awayinserts of cemented carbide (type: CNMG120408, CNMG432, with chipbreaker)

Composition of Film:

-   TiCrAlN-   TiCrAlSiN-   TiAlN    Composition of Alloy Targets:-   Ti: 10 at %, Cr: 18 at %, Al: 72 at %-   Ti: 12 at %, Cr: 15 at %, Al: 70 at %, Si: 3 at %-   Ti: 50 at %, Al: 50 at %

The bias voltage applied to the substrate was 200 V for TiCrAlN film andTiCrAlSiN film and 50V for TiAlN film. The film-forming conditions werethe same as those in Example 1, except that the substrate temperaturewas 550° C., the arc current was 150 A, and the pressure of the reactantgas (nitrogen gas) was 2.66 Pa.

After the film-forming step was complete, the resulting film wasexamined for wear resistance and composition as follows. Wear resistancewas measured by actual turning with the throw-away insert of cementedcarbide under the following conditions. Wear resistance is rated interms of flank wear (vb, Vb_(max)). The results are shown in Table 7.

Cutting Conditions:

-   -   Work: S45C (raw)    -   Cutting speed: 200 m/min    -   Feed speed: 0.2 mm/turn    -   Depth of cut: 1.5 mm    -   Others: dry cutting, continuous turning    -   Cut length: 12000 meters after 60 minutes

The resulting film was found by analysis with EPMA to have thecomposition of (Ti_(0.1)Cr_(0.22)Al_(0.68))N,(Ti_(0.14)Cr_(0.15)Al_(0.68)Si_(0.03))N, and (Ti_(0.54)Al_(0.46))N. Itwas also found that the resulting film contains a little less Al thanthe target used. The atomic ratio of metal elements and nitrogen atomsin the films was in the range of from 0.9 to 1.1. TABLE 7 Flank wearFlank wear Experiment No. Type of film (Vb: μm) (Vb_(max): μm) 1 TiAlN39.6 158 2 TiCrAlN 35.9 44 3 TiCrAlSiN 34.3 42

It is noted from Table 7 that the coating film meeting the requirementsof the present invention is superior in wear resistance as demonstratedby the small flank wear Vb and Vb_(max) (which is about one-fourth thatof the comparative sample).

Example 8

Film coating was performed on a substrate, namely, a chip of cementedcarbide or a square end mill of cemented carbide (10 mm in diameter,with four edges), which is placed on the holder in the AIP apparatusshown in FIG. 2, by using a target of alloy variously composed of Ti,Cr, Al, and B. With the vacuum chamber evacuated to 2.66 Pa, an arccurrent of 150 A was applied for film forming, so that the surface ofthe substrate was coated with an approximately 3-μm thick (TiAlCrB)Nfilm having the composition shown in Table 8. Incidentally, during filmforming, a bias voltage of 150V was applied to the substrate so as tokeep it negative with respect to earth potential. Other film-formingconditions are the same as those in Example 3. The resulting film wasexamined for the compositional ratio of Ti, Al, Cr, and B by EPMA. Thecontent of metal elements and impurity elements such as O (excluding N)in the film was also determined by EPMA. It was found that the contentof oxygen is less than 1 atom %. The results are shown in Table 8. TABLE8 Oxidation Experi- Worn starting ment Film composition (atomic ratio)width temperature No. Ti Al Cr B N (μm) (° C.) 1 0.13 0.68 0.16 0.03 123 1050 2 0.11 0.70 0.16 0.03 1 25 1050 3 0.11 0.67 0.16 0.06 1 28 10304 0.15 0.645 0.20 0.005 1 33 950

It is noted from Table 8 that the samples Nos. 1 to 3, which are coatedwith a film containing B in an amount specified in the presentinvention, have a higher oxidation starting temperature and better wearresistance (in terms of worn width) in cutting test as compared with thesample No. 4. It is apparent that a hard film with good wear resistanceis obtained if it contains B in an amount specified in the presentinvention.

Example 9

Film coating was performed on a square end mill of cemented carbide (10mm in diameter, with two edges) as a substrate by using a target ofalloy composed of Ti (9 at %), Cr (19 at %), and Al (72 at %) in thesame way as in Example 1. Several (Ti,Al,Cr)N films varying in crystalorientation were formed at varied bias voltage and film-formingtemperature. Also, several (Ti,Al,Cr)(CN) films varying in the ratio ofC and N were formed by using a mixture gas of nitrogen and methane asthe film-forming gas. Further, several layered films composed of(Ti,Al,Cr)N film and Ti₅₀Al₅₀N film were formed. The sample No. 8 inTable 9 is a layered film composed of (Ti,Al,Cr)(CN) film and Ti₅₀Al₅₀Nfilm, which were sequentially formed on the surface of the end mill ofcemented carbide. The sample No. 9 in Table 9 is a layered film composedof ten (Ti,Al,Cr)(CN) films and ten Ti₅₀Al₅₀N films, which werealternately formed on the surface of the end mill of cemented carbide.The layered film had a total thickness of about 3 μm. The resultingsamples were examined for wear resistance by cutting in the same way asin Example 2. Wear resistance was rated in terms of worn width. Theresults are shown in Table 9. TABLE 9 Atomic ratio of C and N Film otherthan Experiment in (Ti,Cr,Al)(CN) film (Ti,Cr,Al)(CN) Total Worn widthNo. C N film layers I(111)/I(220) I(200)/I(220) (μm) 1 0 1 None 1 7.7 426 2 0 1 None 1 0.8 3 25 3 0 1 None 1 0.8 0.8 45 4 0.1 0.9 None 1 — — 285 0.25 0.75 None 1 — — 31 6 0.55 0.45 None 1 — — 45 7 0.7 0.3 None 1 — —57 8 0 1 Ti_(0.5)Al_(0.5)N 2 — — 28 9 0 1 Ti_(0.5)Al_(0.5)N 20 — — 27

It is noted from Table 9 that samples Nos. 3, 6, and 7 are superior inwear resistance as indicated by the large worn width. This suggests thatthe coating film has good wear resistance if the crystal orientation andthe C/N ratio in the (Ti,Al,Cr)(CN) film are so controlled as to meetthe requirements of the present invention.

Example 10

Film coating was performed on a square end mill of cemented carbide (10mm in diameter, with two edges) or a chip of cemented carbide by using atarget of alloy composed of Ti (10 at %), Cr (18 at %), and Al (72 at%). An approximately 3-μm thick (Ti,Al,Cr)N film was formed on thesubstrate by using the AIP apparatus shown in FIG. 2, with the biasvoltage, substrate temperature, and nitrogen gas pressure varied asshown in Tables 10 and 11. The arc current at the time of film formingwas 150 A, and other conditions were the same as those in Example 1.

After the film-forming step was complete, the coating film was examinedfor metal composition, crystal structure, crystal orientation, X-raydiffraction, Vickers hardness, and wear resistance. (The data of X-raydiffraction include the angle of diffraction and the half width of peaksdue to the (111) plane of sodium chloride structure.) X-raydiffractometery was carried out by θ-2θ method with Cu Kα line. Wearresistance was measured (in terms of worn width) by cutting test in thesame way as in Example 2. The composition of metal components in thecoating film was analyzed by EPMA. It was found as shown in Table 11that the composition slightly fluctuates as follows depending on thefilm-forming conditions.

-   Ti: 10-12 at %, Cr: 20-23 at %, and Al: 66-68 at %

The results of this example are summarized in Tables 10 and 11.Quantitative analyses by EPMA for metal elements and impurity elementsin the coating film show that the amount of oxygen and carbon is lessthan 1 atom % and less than 2 atom %, respectively, and the atomic ratioof total metal elements to nitrogen was from 0.9 to 1.1. TABLE 10Nitrogen Experi- Bias Substrate gas Value of Angle of ment voltagetemperature pressure expression I(200)/ I(111)/ I(200)/ diffraction HalfWorn No. (V) (° C.) (Pa) (4) I(111) I(220) I(220) (°)* width Hardnesswidth 1 50 550 2.66 0.87 1.4 2.4 3.4 37.66 0.72 3050 29.8 2 75 550 2.661 1.0 3.0 2.9 37.51 0.62 3200 23.5 3 100 550 2.66 1 0.2 9.5 2.1 37.480.52 3300 20.1 4 150 550 2.66 1 1.2 9.6 11.8 37.57 0.45 3350 18.7 5 200550 2.66 1 5.6 2.2 12.4 37.51 0.60 3200 23.5 6 250 550 2.66 1 6.5 2.013.3 37.53 0.51 3150 25.4 7 400 550 2.66 Excessively — — — — —Excessively EExcessively thin film thin film thin film 8 150 550 0.30 12.1 7.5 16.0 37.55 0.55 2900 38.4 9 150 550 1.33 1 1.8 8.8 15.9 37.570.50 3200 23.5 10 150 550 2.66 1 1.2 9.6 11.8 37.57 0.45 3350 18.7 11150 550 3.99 1 0.8 9.5 7.3 37.55 0.47 3300 20.1 12 150 550 5.2 1 1.1 6.36.8 37.59 0.45 3250 21.7 13 150 550 7.8 Excessively — — — — —Excessively Excessively thin film thin film thin film 14 150 250 2.66Film — — — — — Film Film peeled peeled peeled 15 150 450 2.66 1 2.1 6.713.7 37.58 3200 23.5 16 150 550 2.66 1 1.2 9.6 11.8 37.57 0.45 3300 20.117 150 650 2.66 0.96 0.7 11.8 7.7 37.41 0.71 3300 20.1 18 150 850 2.660.9 0.5 12.8 6.8 37.30 2950 35.3Target: TiAlCr (Ti:Al:Cr = 10:72:18), * angle of diffraction due to(111) plane.

TABLE 11 Experi- Bias Substrate Nitrogen Composition of film mentvoltage tempera- gas pres- (atomic ratio) No. (V) ture (° C.) sure (Pa)Ti Cr Al 1 50 550 2.66 0.10 0.21 0.69 2 75 550 2.66 0.11 0.22 0.67 3 100550 2.66 0.11 0.22 0.67 4 150 550 2.66 0.11 0.22 0.66 5 200 550 2.660.12 0.22 0.66 6 250 550 2.66 0.12 0.22 0.66 7 400 550 2.66 Excessivelythin film 8 150 550 0.3 0.12 0.22 0.66 9 150 550 1.33 0.12 0.22 0.66 10150 550 2.66 0.11 0.22 0.66 11 150 550 3.99 0.11 0.22 0.66 12 150 5505.2 0.11 0.22 0.66 13 150 550 7.8 Excessively thin film 14 150 250 2.66Film peeled 15 150 450 2.66 0.11 0.22 0.67 16 150 550 2.66 0.11 0.220.66 17 150 650 2.66 0.10 0.21 0.69 18 150 850 2.66 0.10 0.20 0.70

It is noted from Tables 10 and 11 that the samples Nos. 1 to 6, 9 to 12,and 15 to 17, which were prepared at an adequately controlled biasvoltage, reactant gas pressure, and substrate temperature according tothe present invention are superior in hardness and wear resistance (interms of worn width) to the samples Nos. 7, 8, 13, 14, and 18. Thissuggests that the coating film has the crystal orientation, the angle ofdiffraction, and the half width as desired if the film formingconditions are controlled as specified in the present invention. Thusthe resulting film has outstanding wear resistance.

Example 11

Film coating was performed on a square end mill of cemented carbide (10mm in diameter, with four edges), a chip of cemented carbide, and apiece of platinum foil (0.1 mm thick) by using a target of alloycomposed of Ti (12 at %), Cr (15 at %), Al (70 at %), and Si (3 at %).An approximately 3-μm thick (Ti,Cr,Al,Si)N film was formed on thesubstrate by using the AIP apparatus shown in FIG. 2, with the biasvoltage, substrate temperature, and nitrogen gas pressure varied asshown in Tables 12 and 13. The arc current at the time of film formingwas 150 A, and other conditions were the same as those in Example 3.

After the film-forming step was complete, the coating film was examinedfor metal composition, crystal structure, crystal orientation, X-raydiffraction, Vickers hardness, and wear resistance. (The data of X-raydiffraction include the angle of diffraction and the half width of peaksdue to the (111) plane of sodium chloride structure.) X-raydiffractometery was carried out by θ-2θ method with Cu Kα line. Wearresistance was measured (in terms of worn width) by cutting test in thesame way as in Example 4. The composition of metal components in thecoating film was analyzed by EPMA. It was found that the oxidationstarting temperature of the film formed on the platinum foil was higherthan 1100° C. TABLE 12 Nitrogen Angle Experi- Bias Substrate gas Valueof of ment voltage temperature pressure Crystal expression I(200)/I(111)/ I(200)/ diffraction Worn No. (V) (° C.) (Pa) structure (4)I(111) I(220) I(220) (°)* Hardness width 1 50 550 2.66 B + H 0.53 — — —— 2934 29.0 2 75 585 2.66 B + H 0.6 — — — — 3127 21.1 3 100 577 2.66 B 10.42 1.24 0.52 37.07 3127 21.1 4 125 600 2.66 B 1 0.47 2.65 1.25 36.983210 18.5 5 150 594 2.66 B 1 1.83 2.01 3.68 37.06 3296 16.2 6 200 6122.66 B + H 0.8 3.17 1.69 5.35 37.03 3127 21.1 7 250 624 2.66 B + H 0.73.73 1.72 6.40 37.0.1 3210 18.5 8 350 650 2.66 B + H 0.75 7.82 0.80 6.2237.04 3210 18.5 9 450 680 2.66 Excessively Excessively — — — —Excessively Excessively thin film thin film thin film thin film 10 150580 0.30 B + H 0.45 3.25 5.77 18.75 36.92 2950 28.2 11 150 580 1.33 B 12.12 5.38 11.36 37.01 3296 16.2 12 150 580 3.99 B 1 1.44 2.38 3.43 37.063296 16.2 13 150 580 7.80 Excessively Excessively — — — — ExcessivelyExcessively thin film thin film thin film thin film 14 150 250 2.66 FilmFilm — — — — Film Film peeled peeled peeled peeled 15 150 480 2.66 B 11.90 1.51 2.86 37.09 3210 18.5 16 150 520 2.66 B 1 0.85 3.02 2.56 37.063230 17.9 17 150 660 2.66 B + H 0.8 0.68 3.16 2.14 37.06 3250 17.4 18150 850 2.66 B + H 0.4 0.64 3.45 2.21 37.02 2950 28.2Target: TiCrAlSi (Ti:Cr:Al:Si = 12:15:70:3),*angle of diffraction due to (111) plane.

TABLE 13 Experi- Bias Substrate Nitrogen Composition of film mentvoltage tempera- gas pres- (atomic ratio) No. (V) ture (° C.) sure (Pa)Ti Cr Al Si 1 50 560 2.66 0.127 0.168 0.684 0.021 2 75 585 2.66 0.1290.171 0.673 0.027 3 100 577 2.66 0.130 0.171 0.667 0.032 4 125 600 2.660.136 0.164 0.673 0.027 5 150 594 2.66 0.131 0.158 0.683 0.028 6 200 6122.66 0.130 0.152 0.680 0.038 7 250 624 2.66 0.133 0.155 0.682 0.030 8350 650 2.66 0.136 0.154 0.684 0.026 9 450 660 2.66 Excessively thinfilm 10 150 580 0.30 0.125 0.155 0.691 0.029 11 150 580 1.33 0.129 0.1590.684 0.028 12 150 580 3.99 0.139 0.176 0.658 0.027 13 150 580 7.80Excessively thin film 14 150 250 2.66 Film peeled 15 150 480 2.66 0.1300.169 0.673 0.028 16 150 520 2.66 0.134 0.159 0.681 0.026 17 150 6602.66 0.133 0.165 0.672 0.030 18 150 850 2.66 0.135 0.174 0.662 0.029

It is noted from Tables 12 and 13 that the samples Nos. 1 to 8, 11, 12,and 15 to 17, which were prepared at an adequately controlled biasvoltage, reactant gas pressure, and substrate temperature according tothe present invention are superior in wear resistance (in terms of wornwidth) to the samples Nos. 9, 10, 13, 14, and 18. This suggests that thecoating film has the crystal orientation, the angle of diffraction, andthe half width as desired if the film forming conditions are controlledas specified in the present invention. Thus the resulting film hasoutstanding wear resistance.

Example 12

Film coating was performed on a square end mill of cemented carbide (10mm in diameter, with two edges) by using a target of alloy composed ofTi (10 at %), Cr (18 at %), and Al (72 at %). A multi-layered film ofmetal nitride, carbide, carbonitride, or metal as shown in Table 14 wasformed on the substrate by using the AIP apparatus (having twoevaporating sources) as shown in FIG. 2. The arc current was varied from100 A to 150 A, the pressure of the reactant gas (nitrogen or a mixtureof nitrogen and methane) was varied from 0 Pa (for metal film) to 2.66Pa, the bias voltage applied to the substrate was varied from 30V to150V according to the kind of film, and the substrate temperature waskept at 550° C., with other conditions remaining the same as those inExample 1. The multi-layered film was formed by repeating alternatecoating with film-1 and film-2 (specified in Table 14) from twoevaporating sources. The number of layers shown in Table 14 is countedby regarding “film-1+film-2” as one unit. The total thickness of themulti-layered film was about 3 am. After the film-forming step wascomplete, the coating film was examined for wear resistance by cuttingtest in the same way as in Example 2. The results are shown in Table 14.TABLE 14 Experiment Thickness of Thickness of Number Worn width No.Film-1 ** film-1 (μm) Film-2 film-2 (μm) of layers (μm) 1Ti_(0.5)Al_(0.5)N 0.5 TiAlCrN * 2.5 1 25 2 Ti_(0.5)Al_(0.5)N 0.05TiAlCrN * 0.05 30 27 3 Ti_(0.5)Al_(0.5)N 0.005 TiAlCrN * 0.005 300 26 4TiN 0.5 TiAlCrN * 2.5 1 26 5 TiN 0.05 TiAlCrN * 0.05 30 28 6 TiN 0.005TiAlCrN * 0.005 300 26 7 Ti_(0.5)Al_(0.5) 0.01 TiAlCrN * 3 1 27 8 Ti 0.1TiAlCrN * 3 1 25 9 Cr 1 TiAlCrN * 2 1 26 10 TiAlCrN * 1.5Ti_(0.08)Al_(0.74)Cr_(0.18)N 1.5 1 25 11 TiAlCrN * 0.05Ti_(0.08)Al_(0.74)Cr_(0.18)N 0.05 30 26 12 TiAlCrN * 0.005Ti_(0.1)Al_(0.75)Cr_(0.15)N 0.005 300 25* Formed from a TiAlCrN target (Ti:Al:Cr = 10:72:18)** Formed directly on the substrate

It is noted from Table 14 that the multi-layered coating film exhibitsoutstanding wear resistance (in terms of worn width not larger than 30am) so long as each layer meets the requirements of the presentinvention.

Example 13

In order to demonstrate the effect of multi-layer film, coating with aTi0.5Al_(0.5)N or Ti(C_(0.5)N_(0.5)) film was made on the coating film(pertaining to the present invention) of each of the end mill samplesNos. 3, 5, 8, 10, and 12 in Example 3. Coating with two films wasrepeated alternately. The kind of film and the number of layers areshown in Table 15. The total thickness of the multi-layer film was about3 μm. The thus obtained coating film was examined for wear resistance bycutting test in the same way as in Example 4. The results are shown inTable 15. TABLE 15 Experiment Multi-layer structure Number of No. (upperlayer/lower layer) layers Worn width (μm) 3Ti_(0.02)Cr_(0.1)Al_(0.85)Si_(0.03)N/Ti(C_(0.5)N_(0.5)) 2 32 5Ti_(0.1)Cr_(0.18)Al_(0.72)N/Ti_(0.5)Al_(0.5)N 10 23 8Ti_(0.11)Cr_(0.15)Al_(0.71)Si_(0.03)N/Ti_(0.5)Al_(0.5)N 2 16 10Ti_(0.13)Cr_(0.15)Al_(0.70)Si_(0.02)N/Ti_(0.5)Al_(0.5)N 10 15 12Ti_(0.18)Cr_(0.08)Al_(0.71)Si_(0.03)C_(0.2)N_(0.8)/Ti_(0.5)Al_(0.5)N 1018

It is noted from Table 15 that the multi-layered coating film (in thesamples Nos. 5, 8, 10, and 12) exhibits better wear resistance (in termsof worn width) than the sample No. 3 so long as each layer meets therequirements of the present invention.

Example 14

Film coating was performed on a square end mill of cemented carbide (10mm in diameter, with four edges) by using a target of alloy composed ofTi (12 at %), Cr (15 at %), Al (70 at %), and Si (3 at %). Amulti-layered film of metal nitride, carbide, carbonitride, or metal asshown in Table 16 was formed on the substrate by using the AIP apparatus(having two evaporating sources) as shown in FIG. 2. The arc current wasvaried from 100 A to 150 A, the pressure of the reactant gas (nitrogenor a mixture of nitrogen and methane) was varied from 0 Pa (for metalfilm) to 2.66 Pa, the bias voltage applied to the substrate was variedfrom 30V to 150V according to the kind of film, and the substratetemperature was kept at 550° C., with other conditions remaining thesame as those in Example 3. The multilayered film was formed byrepeating alternate coating with film-1 and film-2 (specified in Table16) from two evaporating sources. The number of layers shown in Table 16is counted by regarding “film-1+film-2” as one unit. The total thicknessof the multi-layered film was about 3 μm. After the film-forming stepwas complete, the coating film was examined for wear resistance bycutting test in the same way as in Example 4. The results are shown inTable 16. Incidentally, the TiAlCrSiN film was found to contain metalelements in a ratio of Ti: 13 at %, Al: 68 at %, Cr: 16 at %, and Si: 3at %. TABLE 16 Experiment Thickness of Thickness of Number of Worn widthNo. Film-1** film-1 (μm) Film-2 film-2 (μm) layers (μm) 1Ti_(0.5)Al_(0.5)N 0.5 TiAlCrSiN * 2.5 1 20 2 Ti_(0.5)Al_(0.5)N 0.05TiAlCrSiN * 0.05 30 21.6 3 Ti_(0.s)Al_(0.5)N 0.005 TiAlCrSiN * 0.005 30020.8 4 TiN 0.5 TiAlCrSiN * 2.5 1 20.8 5 TiN 0.05 TiAlCrSiN * 0.05 3022.4 6 TiN 0.005 TiAlCrSiN * 0.005 300 20.8 7 Ti_(0.5)Al_(0.5) 0.01TiAlCrSiN * 3 1 21.6 8 Ti 0.1 TiAlCrSiN * 3 1 20 9 Cr 1 TiAlCrSiN * 2 120.8 10 TiAlCrSiN * 1.5 Ti_(0.13)Al_(0.7)Cr_(0.15)Si_(0.02)N 1.5 1 20 11TiAlCrSiN * 0.05 Ti_(0.13)Al_(0.7)Cr_(0.15)Si_(0.02)N 0.05 30 20.8 12TiAlCrSiN * 0.005 Ti_(0.1)Al_(0.74)Cr_(0.14)Si_(0.02)N 0.005 300 20* Formed from a TiAlCrSiN target (Ti:Al:Cr:Si = 12:70:15:3).** Formed directly on the substrate

It is noted from Table 16 that the multi-layered coating film (in thesamples Nos. 1 to 12) exhibits good wear resistance (in terms of wornwidth smaller than 30 μm) so long as each layer meets the requirementsof the present invention.

Example 15

Film coating was performed on a chip of cemented carbide or a square endmill of cemented carbide (10 mm in diameter, with two edges) by using atarget of alloy composed of Ti (9 at %), Cr (19 at %), and Al (72 at %).The conditions of film coating were the same as those in Example 1except that the duration of film forming was 30 minutes, the arc currentwas 100 A, the substrate temperature was 500° C., and the bias voltagewas varied in the range of 50V to 400V so that the substrate was keptnegative with respect to earth potential. The resulting film wasexamined for crystal structure by X-ray diffraction. The coated chip wasbroken and the fracture surface was observed under a scanning electronmicroscope to measure the thickness of the coating film. The coatingfilm was examined for wear resistance by cutting test in the same way asin Example 2. The results are shown in Table 17. Incidentally, theanalysis by EMPA revealed that the coating film is composed of Ti: 9-11at %, Cr: 19-21 at %, and Al: 68-71 at %, depending on the bias voltageapplied at the time of film forming. TABLE 17 Bias Film Experimentvoltage thickness Crystal Worn width No. (V) (μm) structure * (μm) 1 504.3 B1 + Hex 35 2 70 4.1 B1 25 3 150 3.8 B1 20 4 250 3.3 B1 22 5 300 2.5B1 23 6 350 0.7 B1 29 7 400 Film forming Not identified — almostimpossible* B1 represents sodium chloride structure, and Hex represents ZnSstructure.

It is noted from Table 17 that the samples Nos. 2 to 5, which wereprepared with a bias voltage within the range specified by the presentinvention, have the optimum crystal structure and film thickness. Bycontrast, the sample No. 1, which was prepared with a bias voltage lowerthan that specified in the present invention, has a mixed crystalstructure of B1 and Hex and hence is poor in wear resistance. Also, thesamples Nos. 6 and 7, which were prepared with a bias voltage higherthan that specified in the present invention, have a thin film. Thosesamples meeting the requirements (for bias voltage) of the presentinvention were superior in wear resistance.

Example 16

Film coating (approximately 3 μm thick) was performed on substrates byusing the AIP apparatus shown in FIG. 2. The substrates, the compositionof film, and the composition of alloy targets are shown below.

Substrates:

-   Chips of cemented carbide, or ball end mill of cemented carbide (10    mm in diameter, 5 mm in center radius, with two edges)    Composition of Film:-   TiAlCrN, TiAlN, TiN, or CrN    Composition of Alloy Targets:-   Ti: 10 at %, Cr: 18 at %, Al: 72 at %; Ti: 50 at %, Al: 50 at %;    pure Ti metal; or pure Cr metal

The bias voltage applied to the substrate was 150 V for TiAlCrN film and50V for TiAlN film or TiN film. The film-forming conditions were thesame as those in Example 1, except that the substrate temperature wasvaried from 550° C. to 580° C., the arc current was 150 A, and thepressure of the reactant gas (nitrogen gas) was 2.66 Pa.

After the film-forming step was complete, the resulting film wasexamined for composition, Vickers hardness, and wear resistance. Wearresistance was measured by actual cutting under the followingconditions. Wear resistance is rated in terms of the worn width at thetip of the ball end mill and the worn width at the boundary.

Cutting Conditions:

-   -   Work: S55C (with a Brinell hardness of 220)    -   Cutting speed: 100 m/min    -   Feed speed: 0.05 mm/edge    -   Depth of cut: 4.5 mm    -   Pick feed: 0.5 mm    -   Cut length: 30 meters

Analyses by EPMA revealed that the resulting TiCrAlN film and TiAlN filmhave the composition of (Ti_(0.1)Cr_(0.22)Al_(0.61))N andTi_(0.54)Al_(0.46))N, respectively, in which the amount of Al isslightly less than that in the alloy target. The atomic ratio of metalelements and nitrogen atoms in the films was in the range of from 0.9 to1.1. TABLE 18 Bias Pressure Worn Worn Experiment voltage Temperature ofreactant Hardness width of width at No. Film (V) (° C.) gas (Pa) offilmtip (μm) boundary (μm) 1 TiAlCrN *¹ 150 550 2.66 3250 152 48 2 TiAlN *²50 550 2.66 2900 320 85 3 TiN 50 550 2.66 2300 188 491 4 CrN 50 550 2.661450 370 571*¹ Target: TiAlCr (Ti:Al:Cr = 10:72:18)*² Target: TiAl (Ti:Al = 50:50)

It is noted from Table 18 that the coating film meeting the requirementsof the present invention is superior to conventional TiAlN, TiN, and CrNfilms as indicated by the smaller amount of wear at the tip and at theboundary in the cutting test with S55C (HB 220).

Example 17

A series of experiments were carried out as follows to see howdischarging is affected at the time of film forming by the relativedensity of the target and the content of impurities in the target.Targets each having the composition shown in Table 19 were prepared froma mixture of Ti powder, Cr powder, and Al powder (all under 100 mesh) byHIP (hot isostatic pressing) at 900° C. and 8×10⁷ Pa. The composition ofthe target was determined by ICP-MS. The target, measuring 254 mm inoutside diameter and 5 mm in thickness, was tested for dischargingcharacteristics by reactive sputtering (with nitrogen reactant gas at500 W) to form a film (3 μm thick) on a chip of cemented carbide.

The resulting hard film was analyzed by XPS and examined for wearresistance by cutting test under the following conditions. The state ofdischarging at the time of film forming was evaluated by visuallyobserving how discharge occurs on the surface and by monitoring thedischarge voltage. The results are shown in Table 19.

Cutting Conditions:

-   -   Work: JIS-SKD61 (HRC50)    -   End mill: cemented carbide, with four edges    -   Cutting speed: 200 m/min    -   Depth of cut: 1 mm    -   Feed speed: 0.05 mm/edge    -   Length of cut: 20 m        Rating of Wear Resistance:    -   ⊚: face wear less than 25 μm    -   ◯: face wear ranging from 25 μm to 50 μm    -   Δ: face wear not less than 50 μm        Rating of Discharging State:    -   Stable: there is no instantaneous increase in discharge voltage,        or there is no uneven distribution of discharges from one place        to another.    -   Slightly unstable: there is an instantaneous increase in        discharge voltage, or there is some uneven distribution of        discharges from one place to another.    -   Unstable: there is a considerable instantaneous increase in        discharge voltage, or there is considerable uneven distribution        of discharges from one place to another.

Interrupted: there is an interruption of discharge during operation.TABLE 19 Relative Rate of film Experi- Composition of target (atomicratio) density State of Composition of film (atomic ratio) forming Wearment No. Ti Cr Al (%) discharge Ti Cr Al (μm/h) resistance 1 0.26 0.060.68 99.8 stable 0.26 0.06 0.68 1.50 ⊚ 2 0.20 0.07 0.73 99.5 stable 0.200.07 0.73 1.61 ⊚ 3 0.18 0.06 0.76 99.2 stable 0.18 0.06 0.76 1.68 ◯ 40.08 0.14 0.78 99.2 stable 0.08 0.14 0.78 1.72 ◯ 5 0.01 0.18 0.81 99.6stable 0.01 0.18 0.81 1.79 ◯ 6 0.17 0.11 0.72 99.7 stable 0.17 0.11 0.721.59 ⊚ 7 0.08 0.18 0.74 99.0 stable 0.08 0.18 0.74 1.63 ⊚ 8 0.26 0.060.68 94.0 unstable 0.24 0.12 0.62 1.50 Δ 9 0.08 0.14 0.78 92.3 unstable0.12 0.16 0.70 1.72 Δ 10 0.17 0.11 0.72 90.2 interrupted not measurable

It is noted from Table 19 that the samples Nos. 1 to 7, which have therelative density meeting the requirements of the present invention,permit satisfactory discharging. As the result they yielded coating filmsuperior in wear resistance and having the same composition as thetarget. It is also noted from Table 19 that the samples Nos. 8 to 10,which have the relative density outside the range specified in thepresent invention, gave unstable discharge or caused discharge to beinterrupted. As the result, they yielded coating film poor in wearresistance and having the composition greatly different from that of thetarget.

Example 18

A series of experiments were carried out as follows to see howdischarging is affected at the time of film forming by the relativedensity of the target and the content of impurities in the target.Targets each having the composition shown in Table 20 were prepared froma mixture of Ti powder, Cr powder, Al powder, and Si powder (all under100 mesh) by HIP (hot isostatic pressing) at 900° C. and 8×10⁷ Pa. Thecomposition of the target was determined by IcP-MS. The target,measuring 254 mm in outside diameter and 5 mm in thickness, was testedfor discharging characteristics by reactive sputtering (with nitrogenreactant gas at 500 W) to form a film (about 3 μm thick) on a chip ofcemented carbide.

The resulting hard film was analyzed by XPS and examined for wearresistance by cutting test under the following conditions. The state ofdischarging at the time of film forming was evaluated by visuallyobserving how discharge occurs on the surface and by monitoring thedischarge voltage. The results are shown in Table 20.

Cutting Conditions:

-   -   Work: JIS-SKD61 (HRC50)    -   End mill: cemented carbide, with four edges    -   Cutting speed: 20 m/min    -   Depth of cut: 1 mm    -   Feed speed: 0.05 mm/edge    -   Length of cut: 30 m        Rating of Wear Resistance:    -   ◯: face wear less than 20 μm    -   xface wear not less than 20 μm        Rating of Discharging State:    -   Stable: there is no instantaneous increase in discharge voltage,        or there is no uneven distribution of discharges from one place        to another.    -   Slightly unstable: there is an instantaneous increase in        discharge voltage, or there is some uneven distribution of        discharges from one place to another.    -   Unstable: there is a considerable instantaneous increase in        discharge voltage, or there is considerable uneven distribution        of discharges from one place to another.

Interrupted: there is an interruption of discharge during operation.TABLE 20 Relative Experi- Composition of target (atomic ratio) densityState of Composition of film (atomic ratio) Wear ment No. Ti Cr Al Si(%) discharge Ti Cr Al Si resistance 1 0.28 0.18 0.52 0.02 99.8 stable0.30 0.18 0.50 0.02 ◯ 2 0.10 0.15 0.72 0.03 99.5 stable 0.11 0.15 0.710.03 ◯ 3 0.02 0.20 0.72 0.06 99.2 stable 0.04 0.20 0.70 0.06 ◯ 4 0.110.15 0.72 0.02 99.2 stable 0.13 0.15 0.70 0.02 ◯ 5 0.16 0.08 0.73 0.0399.6 stable 0.18 0.08 0.71 0.03 ◯ 6 0.16 0.08 0.73 0.03 99.7 stable 0.180.08 0.71 0.03 ◯ 7 0.16 0.08 0.73 0.03 99.0 stable 0.18 0.08 0.71 0.03 ◯8 0.10 0.15 0.72 0.03 94.0 unstable 0.10 0.20 0.65 0.05 X 9 0.11 0.150.72 0.02 92.3 unstable 0.19 0.25 0.55 0.01 X 10 0.16 0.08 0.73 0.0390.2 interrupted Not measurable

It is noted from Table 20 that the samples Nos. 1 to 7, which have therelative density meeting the requirements of the present invention,permit satisfactory discharging. As the result they yielded coating filmsuperior in wear resistance and having the same composition as thetarget. It is also noted from Table 20 that the samples Nos. 8 to 10,which have the relative density outside the range specified in thepresent invention, gave unstable discharge or caused discharge to beinterrupted. As the result, they yielded coating film poor in wearresistance and having the composition greatly different from that of thetarget.

Example 19

Targets each having the composition shown in Table 21 were prepared froma mixture of Ti powder (under 100 mesh), Cr powder (under 100 mesh), andAl powder (under 240 mesh) by HIP (hot isostatic pressing) at 500-900°C. and 8×10⁷ Pa. To the bottom of the target was attached by brazing aflange (104 mm in outside diameter and 2 mm in thickness) which is acopper backing plate. (Alternatively, the flange was formed by machiningthe target.) The target was mounted on an ion-plating apparatus of arcdischarge type. Using this target, a 3-μm thick film was formed on achip of cemented carbide under the following conditions.

-   Reactant gas: nitrogen or a mixture of nitrogen and methane.-   Substrate temperature: 500° C.-   Arc current: 100 A-   Bias voltage applied to the substrate: 150V

The target was analyzed for composition by ICP-MS. The film was examinedfor wear resistance by cutting test in the same way as in Example 17.Analyses by XPS revealed that the resulting film has almost the samecomposition as that of the target (with a difference within ±2 at %).The target was examined for voids (defects) and their size by ultrasonictest. The state of discharging at the time of film forming was evaluatedin the same way as in Example 17. The results are shown in Table 21.TABLE 21 Experi- Composition of target (atomic ratio) Relative BackingState of Rate of film Wear ment No. Ti Cr Al density (%) Voids (size)plate discharging forming (μm/h) resistance 1 0.26 0.06 0.68 99.8 <0.3mm no stable 3.20 ⊚ 2 0.20 0.07 0.73 99.5 <0.3 mm no stable 3.44 ⊚ 30.18 0.06 0.76 99.2 <0.3 mm no stable 3.58 ◯ 4 0.08 0.14 0.78 98.2 <0.3mm no stable 3.67 ◯ 5 0.01 0.18 0.81 96.5 voids not smaller no unstable3.81 Δ than 0.3 mm 6 0.17 0.11 0.72 92.7 voids not smaller nointerrupted — — than 0.3 mm 7 0.08 0.18 0.74 97.0 voids not smaller noslightly 3.43 ⊚ than 0.3 mm unstable 8 0.26 0.06 0.68 94.1 voidspenetrating no interrupted — — from front to back 9 0.08 0.14 0.78 92.3<0.3 mm yes unstable 3.67 Δ 10 0.17 0.11 0.72 90.2 <0.3 mm yesinterrupted — Not measurable

It is noted from Table 21 that the samples Nos. 1 to 4, which meet therequirements for the relative density of the target and the size ofvoids in the target as specified in the present invention, permit stabledischarging at the time of film forming and yield film with good wearresistance. By contrast, in the case of the samples Nos. 5 and 7, whichdo not meet the requirements for the size of voids in the target asspecified in the present invention, the samples Nos. 9 and 10, which donot meet the requirements for the relative density of the target asspecified in the present invention, and the samples Nos. 6 and 8, whichdo not meet the requirements for the relative density of the target andthe size of voids in the target as specified in the present invention,discharging was unstable or interrupted at the time of film forming andfilm forming was impossible to carry out or the resulting film was poorin wear resistance.

Example 20

Targets each having the composition shown in Table 22 were prepared froma mixture of Ti powder (under 100 mesh), Cr powder (under 100 mesh), Alpowder (under 240 mesh), and Si powder (under 100 mesh) by HIP (hotisostatic pressing) at 500-900° C. and 8×10⁷ Pa. To the bottom of thetarget was attached by brazing a flange (104 mm in outside diameter and2 mm in thickness) which is a copper backing plate. (Alternatively, theflange was formed by machining the target.) The target was mounted on anion-plating apparatus of arc discharge type. Using this target, anapproximately 3-m thick film was formed on a chip of cemented carbideunder the following conditions.

-   Reactant gas: nitrogen or a mixture of nitrogen and methane.-   Substrate temperature: 500° C.-   Arc current: 100 A-   Bias voltage applied to the substrate: −150V

The target was analyzed for composition by atomic absorptionspectrometry. The film was examined for wear resistance by cutting testin the same way as in Example 18. Analyses by XPS revealed that theresulting film has almost the same composition as that of the target(with a difference within ±2 at %). The target was examined for voids(defects) and their size by ultrasonic test. The state of discharging atthe time of film forming was evaluated in the same way as in Example 18.The results are shown in Table 22. TABLE 22 Experi- Composition oftarget (atomic ratio) Relative Backing State of Wear ment No. Ti Cr AlSi density (%) Voids (size) plate discharging resistance 1 0.28 0.180.52 0.02 99.8 <0.3 mm no stable ◯ 2 0.10 0.15 0.72 0.03 99.5 <0.3 mm nostable ◯ 3 0.02 0.20 0.72 0.06 99.2 <0.3 mm no stable ◯ 4 0.11 0.15 0.720.02 98.2 <0.3 mm no stable ◯ 5 0.28 0.18 0.52 0.02 96.5 voids notsmaller no unstable X than 0.3 mm 6 0.10 0.15 0.72 0.03 92.7 voids notsmaller no interrupted — than 0.3 mm 7 0.02 0.20 0.72 0.06 97.0 voidsnot smaller no slightly ◯ than 0.3 mm unstable 8 0.11 0.15 0.72 0.0294.1 voids penetrating no interrupted — from front to back 9 0.16 0.080.73 0.03 92.3 <0.3 mm yes unstable X 10 0.16 0.08 0.73 0.03 90.2 <0.3mm yes interrupted Not measur- able

It is noted from Table 22 that the samples Nos. 1 to 4, which meet therequirements for the relative density of the target and the size ofvoids in the target as specified in the present invention, permit stabledischarging at the time of film forming and yield film with good wearresistance. By contrast, in the case of the samples Nos. 5 and 7, whichdo not meet the requirements for the size of voids in the target asspecified in the present invention, the samples Nos. 9 and 10, which donot meet the requirements for the relative density of the target asspecified in the present invention, and the samples Nos. 6 and 8, whichdo not meet the requirements for the relative density of the target andthe size of voids in the target as specified in the present invention,discharging was unstable or interrupted at the time of film forming andfilm forming was impossible to carry out or the resulting film was poorin wear resistance.

Example 21

A series of experiments were carried out to investigate how the state ofdischarging at the time of film forming is affected by the content ofimpurities (oxygen, hydrogen, chlorine, copper, and magnesium) in thetarget.

Targets each having the composition shown in Table 23 were prepared inthe same way as in Example 19. All of the resulting targets have arelative density not lower than 99% and are free of voids (larger than0.3 mm) and continuous defects. Using the targets, film forming wascarried out in the same way as in Example 19, except that the reactantgas was nitrogen alone. The amount of impurities in the target wasdetermined by atomic absorption spectrometry. The state of dischargingat the time of film forming was evaluated in the same way as in Example17. TABLE 23 Experi- Composition of target (mass %) State of ment No. TiCr Al O H Cl Cu Mg discharging 1 37.48 10.55 51.60 0.28 0.02 0.03 0.030.01 stable 2 29.97 12.39 57.07 0.31 0.03 0.17 0.04 0.02 slightlyunstable 3 27.76 11.10 60.89 0.07 0.01 0.14 0.01 0.02 stable 4 13.1623.81 62.61 0.22 0.05 0.08 0.03 0.03 stable 5 2.97 30.66 66.16 0.10 0.030.04 0.03 0.01 stable 6 25.42 18.40 55.69 0.26 0.02 0.15 0.05 0.01stable 7 12.76 29.25 57.51 0.28 0.04 0.12 0.02 0.02 stable 8 5.78 32.9361.03 0.14 0.04 0.03 0.04 0.01 stable 9 37.24 17.33 44.95 0.23 0.01 0.190.03 0.02 stable 10 24.00 28.94 46.56 0.33 0.02 0.13 0.01 0.01 stable 1115.03 32.64 51.58 0.52 0.03 0.14 0.04 0.02 slightly unstable 12 13.2340.21 46.20 0.16 0.07 0.10 0.03 0.01 slightly unstable 13 4.76 49.0945.59 0.24 0.01 0.28 0.01 0.02 slightly unstable 14 5.29 47.34 46.900.30 0.03 0.06 0.07 0.01 slightly unstable 15 22.02 35.16 42.33 0.280.02 0.13 0.02 0.04 slightly unstable 16 12.72 46.94 40.12 0.10 0.040.03 0.03 0.02 stable 17 5.11 52.68 41.73 0.25 0.01 0.17 0.04 0.01stable 18 4.74 48.90 45.40 0.66 0.03 0.18 0.03 0.06 slightly unstable 1923.95 28.89 46.48 0.27 0.04 0.22 0.08 0.07 slightly unstable

It is noted from Table 23 that the samples Nos. 1, 3 to 9, 16, and 17,permit good state of discharging, because they meet the requirements forthe content of impurities (oxygen, hydrogen, chlorine, copper, andmagnesium) as specified in the present invention. By contrast, othersamples are poor in state of discharging because they do not meet therequirements specified in the present invention. That is, the samplesNos. 2, 10, and 11 contain oxygen more than specified, the sample No. 12contains hydrogen more than specified, the sample No. 13 containschlorine more than specified, the sample No. 14 contains copper morethan specified, the sample No. 15 contains magnesium more thanspecified, the sample No. 18 contains oxygen and magnesium more thanspecified, and the sample No. 19 contains chlorine, copper, andmagnesium more than specified. This result indicates that it isnecessary that the target should not contain impurities (oxygen,hydrogen, chlorine, copper, and magnesium) more than specified in thepresent invention in order to form the hard film on cutting toolsefficiently under good discharging state during film forming.

Example 22

A series of experiments were carried out to investigate how the state ofdischarging at the time of film forming is affected by the content ofimpurities (oxygen, hydrogen, chlorine, copper, and magnesium) in thetarget.

Targets each having the composition shown in Table 24 were prepared inthe same way as in Example 18. All of the resulting targets have arelative density not lower than 99% and are free of voids (not smallerthan 0.3 mm) and continuous defects. Using the targets, film forming wascarried out in the same way as in Example 18. The amount of impuritiesin the target was determined by atomic absorption spectrometry. Thestate of discharging at the time of film forming was evaluated in thesame way as in Example 18. TABLE 24 Experi- Composition of target (mass%) State of ment No. Ti Cr Al Si O H Cl Cu Mg discharging 1 35.76324.957 37.41 1.50 0.28 0.02 0.03 0.03 0.01 stable 2 14.494 23.601 58.7852.5496 0.31 0.03 0.17 0.04 0.02 slightly unstable 3 2.9431 31.95 59.6825.1771 0.07 0.01 0.14 0.01 0.02 stable 4 15.874 23.497 58.527 1.69230.22 0.05 0.08 0.03 0.03 stable 5 23.632 12.826 60.734 2.5981 0.1 0.030.04 0.03 0.01 stable 6 23.566 12.79 60.563 2.5908 0.26 0.02 0.15 0.050.01 stable 7 23.568 12.792 60.569 2.5911 0.28 0.04 0.12 0.02 0.02stable 8 35.803 24.984 37.454 1.4995 0.14 0.04 0.03 0.04 0.01 stable 914.508 23.622 58.838 2.5519 0.23 0.01 0.19 0.03 0.02 stable 10 2.9431.868 59.532 5.1641 0.33 0.02 0.13 0.01 0.01 slightly unstable 11 15.8223.417 58.327 1.6865 0.52 0.03 0.14 0.04 0.02 slightly unstable 1223.594 12.806 60.64 2.59 0.16 0.07 0.1 0.03 0.01 slightly unstable 1323.549 12.781 60.521 2.589 0.24 0.01 0.28 0.01 0.02 slightly unstable 1423.57 12.793 60.58 2.59 0.3 0.03 0.06 0.07 0.01 slightly unstable 152.963 31.871 59.538 5.1646 0.28 0.02 0.13 0.02 0.04 slightly unstable 1615.904 23.542 58.638 1.6955 0.1 0.04 0.03 0.03 0.02 stable 17 23.56812.792 60.569 2.5911 0.25 0.01 0.17 0.04 0.01 stable 18 23.454 12.7360.28 2.58 0.66 0.03 0.18 0.03 0.06 slightly unstable 19 23.521 12.76660.448 2.5858 0.27 0.04 0.22 0.08 0.07 slightly unstable

It is noted from Table 24 that the samples Nos. 1, 3 to 9, 16, and 17,permit good state of discharging, because they meet the requirements forthe content of impurities (oxygen, hydrogen, chlorine, copper, andmagnesium) as specified in the present invention. By contrast, othersamples are poor in state of discharging because they do not meet therequirements specified in the present invention. That is, the samplesNos. 2, 10, and 11 contain oxygen more than specified, the sample No. 12contains hydrogen more than specified, the sample No. 13 containschlorine more than specified, the sample No. 14 contains copper morethan specified, the sample No. 15 contains magnesium more thanspecified, the sample No. 18 contains oxygen and magnesium more thanspecified, and the sample No. 19 contains chlorine, copper, andmagnesium more than specified. This result indicates that it isnecessary that the target should not contain impurities (oxygen,hydrogen, chlorine, copper, and magnesium) more than specified in thepresent invention in order to form the hard film on cutting toolsefficiently under good discharging state during film forming.

[Effect of the invention] The present invention which specifies thecomposition for Ti, Al, Cr, Si, and B as mentioned above yields hardfilm for cutting tools which is superior in wear resistance toconventional ones. The hard film contributes to long-life cutting toolsfor high-speed cutting and also for cutting hard steel (such as quenchedsteel).

This application is based on patent application Nos. 2001-287587,2001-185464, 2000-402555, 2001-310562, and 2001-185465 filed in Japan,the contents of which are hereby incorporated by references.

1-20. (canceled)
 21. A target for a hard film, which is composed of Ti,Al, Cr, Si, and B, and has a relative density of less than 95%.
 22. Thetarget for a hard film as defined in claim 21, which contains no pores.23. The target for a hard film as defined in claim 21, wherein all porespresent in said target have radius of smaller than 0.3 mm.
 24. Thetarget for a hard film as defined in claim 21, wherein the content ofoxygen is 0.3 mass % or less, the content of hydrogen is 0.05 mass % orless, and the content of chlorine is 0.2 mass % or less.
 25. The targetfor a hard film as defined in claim 24, wherein the content of copper is0.05 mass % or less and the content of magnesium is 0.03 mass % or less.26. The target for a hard film as defined in claim 21, wherein thecontent of copper is 0.05 mass % or less and the content of magnesium is0.03 mass % or less.
 27. The target for a hard film as defined in claim21, wherein said target has a composition defined by(Ti_(1-x-y-z-w), Al_(x), Cr_(y), Si_(z), B_(w)) 0.5≦x≦0.8,0.06≦y,0≦z≦0.1,0≦w≦0.1, 0≦z+w≦0.1, x+y+z+w<1 wherein x, y, z, and w denoterespectively the atomic ratios of Al, Cr, Si, and B.
 28. The target fora hard film as defined in claim 27, which contains no pores.
 29. Thetarget for a hard film as defined in claim 27, wherein all pores presentin said target have radius of smaller than 0.3 mm.
 30. The target for ahard film as defined in claim 27, wherein the content of oxygen is 0.3mass % or less, the content of hydrogen is 0.05 mass % or less, and thecontent of chlorine is 0.2 mass % or less.
 31. The target for a hardfilm as defined in claim 30, wherein the content of copper is 0.05 mass% or less and the content of magnesium is 0.03 mass % or less.
 32. Thetarget for a hard film as defined in claim 27, wherein the content ofcopper is 0.05 mass % or less and the content of magnesium is 0.03 mass% or less.